I made it a habit to get receipts for everything. I couldn't remember what I was going for if I left the computer to get a drink in the kitchen right now
so I have to write everything down. I'll accumulate a week or two's worth of receipts and then reconcile.
I just use a spreadsheet that is set up like a checkbook register. Nothing too fancy.
It took DH a long time to remember to get receipts...but just last week, we were getting gas and the paper was out of their little printer, and he yelled in the cab "you'll have to write this down because the paper is out". I tell ya, it warmed my heart!