Opened jars of salsa or condiments, packages of lunch meat, and/or bottles of juice that you have NO idea how long they've been in the refrigerator and therefore don't know if they are still "good" or not.
While it's true many products have expiration dates on the package, usually once the package/bottle is opened, there is a limited amount of time that you have to use it up before it goes bad (e.g., Bolthouse fruit and veggie juices must be used within 7 days of opening).
When you first open something that you know you won't use in it's entirety the first time, use a sharpie marker and write the date you opened it on the label or on the lid. Then when you pull out that jar of salsa that got pushed to the back of the fridge or that half-eaten package of lunch meat, you'll know with certainty how long it's been in there and whether to eat or toss it.
Wondering how long food lasts in the fridge? Here is a link to the FDA guidelines: