At some point, the Survivalist has to make-do with what he/she has available. If you live 20mi from the hardware store, or further; usually that happens at 4pm on Saturday afternoon when a pipe breaks or some other poorly-timed emergency manifests. Pretty much, you learn to anticipate and lay in basic supplies. Live really far out in the sticks and this is a way of life. So it is with the Survivalist. Self-sufficiency means adapting solutions you have on-hand or going without.
If you need ammunition, you need quality and performance, not just something that works. There are several powders that function with great versatility, and are also excellent in specific applications. Alliant, formerly Hercules, Unique is about the most versatile powder going for Shotgun, handgun, and light rifle or cast bullet rifle loads.
Unique works great in revolver or pistol loads. It won't provide magnum velocities but it will deliver high velocities in small capacity cases like the .45acp and smaller, and when used in magnum revolver cases with cast bullets or at moderate velocities, it performs with economy and excellence. The most useful velocity levels in magnum revolvers is between 900 and 1100 feet per second with a heavy bullet. Most guys can learn double-action shooting with moderate handloads. Being able to control your handgun and hit reliably with a heavy bullet will win the day over a miss with "the most powerful handgun in the world" as Dirty Harry liked to tout the .44rem mag... Usually a load from 8 to 11gr of Unique will deliver all the power you need. Even more functional is to load the heavy bullet in a .38 or .44 Special case, or a .45 Colt. The .454 Casull is primarily a hunter's cartridge so you don't load light loads in this one.
Unique does it all. See the Lyman Cast Bullet Handbook, 3rd edition for all the cast bullet loads you could imagine. Most will include a recipe using Unique. Hard for me to imagine owning a magnum revolver without loading moderate power loads for it. Aside from Brown Bear defense loads, necessary in my backyard, what I want is 1000fps with a 200gr or much heavier bullet. My favorite Casull bullet is a 345gr cast Lyman design. With max loads it penetrates hardwood in terms of feet rather than inches. Huge knockdown power, but recoil prevents fast precision shooting; so the first shot usually must do the trick...
In terms of rifle powders IMR 3031 and 4198 are good choices for small capacity cases and use with cast bullets at fairly high velocities. Any of the 4350 powders is versatile for magnum or .30-06 series cases. I use XMR4350 for its just a bit faster burn rate. Some like the Hogdgons H4350 for its temperature stability. Years ago I bought a bunch of Accurate rifle powders for great price and am still using them. For .22-250 and .308 class cartridges, hard to beat Reloader 15 or Hogdgons Varget. Varget data is also compatible with many magnums, so there is that to consider.
While the competitor or hobby-handloader will choose one powder for a given application, if the Survivalist does this, you run the risk of great variety but no depth of inventory. My basic powders are: Unique, Win 296 for magnum revolver max loads, RL-15 for .223, Varget for .308, and XMR4350 for magnum & 06 cases. Also use IMR/XMR4064. Own one of the super-magnums? You probably want another very slow burnrate powder.
Gearing up? My advice is to study the loading manuals and note the common powders that perform well with your cartridges. Buy those that you can interchange between different applications and you save money and can buy in quantity and save.
If you buy powder and primers over the net, be advised that US Mail won't deliver these materials, so you deal with UPS and they charge a stiff haz-mat fee. Your dealer might combine packaging of primers and powder or they may not. A deal might not be so good if you pay several haz-mat fees on top of freight.
If buying local, look at the lot #s and production dates on the packages. If buying a carton or case of primers, or several cannisters or jugs of powder; you want the lot numbers to match.
Lot numbers are also important if buying precision bullets and expect the same results. 500pk or larger batches of bullets might be important if your aim is utmost accuracy. Nice to match the lot numbers no matter what if buying 2 or more boxes of same bullet.
As far as bullet designs and component interchangeability, there are several rifle and handgun calibers (bore diameter) that allow interchanging handgun bullets for light loads in rifle ctgs. The .357mag and .358win, .35 Whelen and also .358 Norma Magnum are a case in point. Can shoot handgun cast bullets as well. There are lots of .358 rifle bullets in many designs from 200gr flatpoint to 250gr roundnose. For longrange and accuracy, there are 225gr spitzer boattail designs. If you could only own one revolver and rifle for wilderness usage (not self-defense) a heavy framed .357mag and Whelen or Norma magnum would be The Ticket...
Similar combos are the .32H&R magnum and any .30cal rifle. Both shoot .308 bullets. There are no 85gr rifle bullets produced that I'm aware of, but the 85gr .32(handgun) jacketed bullets are .308 dia and would be really explosive on varmints at close range.
Other combos include the .40 cal rifles and either a .40/10mm pistol or .41 magnum. All depends on the bore of your rifle. The .44mag and .444marlin are another choice, but not such a good one in my book unless you go with a bolt rifle in .444Marlin and cast roundnose or pointed bullets which would take a custom mold.
Best values in rifle bullets have always been Sierra BTSP designs, these are marketed under their GameKing and ProHunter label these days. The BTSP, Boat Tail Softpoint designs have very high Ballistic Coefficients and tough jackets. Sierra MatchKing have especially thick jackets. These bullets will out-penetrate hunting bullets on game or other targets. Where I live, I load the Hornady, Nosler, and Sierra BTHP match bullets (not really a hollowpoint, more a hollownose tip) for best ballistic performance and most rugged jacket material.
Hornady spire points offer a great value, as do the non-premium Remington Core-Lokt bullets. I have also favored the Remington BronzePoint bullets over the years along with Winchester Silvertips. The Speer line of Mag-Tip bullets are also very strongly constructed and perform well. Remington's 55gr softpoint is a good tough bullet for non-premium hunting applications in the .223rem. Probably a good choice for whitetail deer in your AR-15 if you can't hunt per regulations with a match bullet like the 75gr hornaday bthp.
I am looking at my woods-walking rifle. A .338-06 loaded with 230gr Nosler Failsafe handloads to max. I am experimenting with a 290gr cast bullet at 2300fps for even better knockdown power and deeper penetration. For versatility the .338 bore offers huge range of bullet weights and highest ballistic performance at reasonable velocity. More bullet development has gone on in the past 15yrs for .338 bore because of the .338 Lapua Magnum and .338 Norma.
When you have a high Ballistic Coefficient bullet, velocity isn't the paramount concern. The .300 and .338 Whisper are .221 Fireball based wildcats often used subsonic for suppressed long distance shooting.