We keep a dry erase board in the kitchen to list both things that need doing and household supplies that need purchasing. Notice that cat litter or paper towels or shampoo is running low? We'll jot it on the board right then while we're thinking of it.
What I've started doing lately before making an errand run is, rather than standing in front of the thing and transcribing the list onto a Post-It note or into my little notepad, I'll just use my phone to snap a picture of it and then call the picture up on the phone's screen while I'm at the store.
It's not like it's any huge time savings, maybe a half-minute, but it feels so Jetsons.