What I do is any time I need a bolt (and can wait to get it) I order a whole box from McMaster. I usually wait until I have a few different bolts to order, to save shipping. I keep them organized by diameter in a plastic parts organizer (e.g. M4, M6, M8, etc.). I only have a couple lengths of each size, and some have an extra head type or two (e.g. flat head, socket head cap screw, pan head, etc.), and it seems like I'm buying them less often because I already have them. You'll see in my parts spreadsheet that I list any (most anyway) bolts I've bought. The parts TM lists out many of the bolts too (e.g. "Bolt, M8 x 40mm", etc.). I've been buying stainless bolts for non-structural things (e.g. for dash bolts, but not for the water pump). I still go to Ace a lot though too, when I know I just need a couple and probably won't need more anytime soon.