9 times out of 10, I get asked if I even -want- the receipt. Which I don't, and they just throw it out. usually it ends up like this, otherwise.
1) Receipt is handed back with card, so I have to take it. Both get pocketed, and when I get home, pockets are emptied, and I usually end up throwing out 2-5 receipts a few days later
2) In the event of a restaurant, I just leave my copy with the signed copy
3) If it goes in the bag, I just throw it out with the bag when I get home
4) If I get handed it separately... I usually just throw it in the bag.
Needless to say, I don't keep my receipts.