For VHF and UHF I store simplex frequencies, generic pairs and local repeaters with tones.
On simplex here in Colorado we have to be aware that bordering states do not follow the same band coordination, so I keep simplex 2m to cover both 15KHz (Colorado for example) and 20KHz (Utah for example) spacing.
Repeater-wise, I keep the local and most used state-wide and will add new ones if I think about it before a trip. I carry an ARRL repeater handbook and will put them in manually otherwise.
There really aren't that many frequencies, especially on 2m. What gets confusing is matching a repeater pair with the right tone. In reality (again using Colorado as an example) there are only 79 2m repeater pairs available and 26 simplex FM voice channels using 15KHz spacing. So in theory you only need to program in 105 memory locations to be able to receive the bulk of FM traffic on 2m. You will almost always have overlap, so a repeater that you use at home will match a repeater pair someplace else.
The problem is there are 42 PL tones, which means that 79 pairs and 42 tones constitute 3,318 combinations to actually be able to talk into a repeater (assuming it's using a tone, most do though). But just to listen you only need the 79 pairs programmed in. I've been able to figure out a tone a couple of ways. Some radios will test or listen for tones to find one that works or you can sometimes call out on 146.520 and ask.