I have the worst track record when it comes to keeping track of opened food items in my fridge

I'll open something, put it back in the fridge, and the next time I see it I have absolutely no idea when I opened it.

The printed date is no help once you've already opened it.

So I throw it out and feel bad about the waste, since I hate risking eating expired food.

Curious if anyone here has a solution to this? Sticky notes, apps, or anything?