Another possiblity is a wallet that has multiiple locations. Just as an example: I only have groceries, dining, hotels on their own cards (eg, a Choice card for Choice hotel stays, so that' easy to remember), plus a card for everything else. I have a fold-out wallet which has a left and right side and three sections on each side. I keep the groceries card on the left bottom, the hotel cards (which the everything else card behind them) on the right bottom, and the dining cards (by that I mean cards linked to RewardsNetwork programs) on the right middle. (I have DL, insurance cards, and other stuff in other sections.)

I don't buy enough stuff in other kinds of stores (eg, drug stores) to bother with a different card there. Double points on just a few dollars a couple times a month is not worth a different card in my opinion. (But of course, everyone's usage pattern at diferent kinds of stores is different, so I'm not saying it wouldn't be worth it for you, I'm just explianing why I don't consider it worth it for me.)

At any case, that's just when I'm not meeting the minimum spend on the signup bonus offer on a new card (which I usually am doing). When I am trying to achieve the minimum spend, that's the one card that I use just about everywhere, and then it's very simple. It goes on the left (in front of the groceries card) until I've met the minimum spend. (Singup bonuses with minimum spend requirements often equate to 10x or 20x or even 50x points/miles/$, and there's no way to match that on any "everyday" card.)

(Who'd have thunk that the more cards you apply for, the simpler it is to know which card to use at any given time!!!)