Don't let the ammo-whores get to you
Buy what you can, rule of thumb has always been 1000 rounds for each gun you have. This amount is at first a goal to achieve, then it becomes your low level limit. Build up a little surplus so you can go shoot when the opportunity presents itself.
My philosophy has always been to buy a little every payday .... 25K of 5.56, 308, 9mm, and 45acp. since mid-2006 ... I usually look for American Eagle/Federal, Wolf Gold, WWB, XTAC, PPU, PMC Bronze in 55 or 62grn... (I used to shoot a lot of Wolf Poly and the stuff in the tan boxes but I am about out of it). Lots of others available, these just seem to be what is in my area. I also have some cans full of green tip... So basically my stash is a large hodge podge of whatever was most cost effective when I bought it. Nice to be able to just grab a can of ammunition and head to the range regardless of what the market is doing. I probably shoot 25% of what I buy/bought and store the rest.
I do have a couple of grab and go cans and for HD I have a couple hundred rounds of 62grn Fusion.
I work on a Naval base so if the SHTF during working hours, I probably wont even make it home...
Stock up, you can always take it to Barter Town...
Sorry to ramble.