Prominent masking tape labels typically solve the problem of "what is that?" in my fridge. It's also one of the reasons I prefer the Emerald Valley salsa containers for leftovers/freezing--they're clear, so I can see the contents
My new dishwasher has never had a problem getting peanut butter smell out, but my old one did. What works best if you don't have a dishwasher: baking soda. Wash the peanut bar first with Dawn (and only Dawn, nothing else degreases as well) and hot, hot water (hot water dissolves the grease). Fill the jar with a bit of Dawn and hot water, and shake the hell out of it. Let it sit until the water is cool. Dump it out, then refill jar with baking soda and hot, hot water. Repeat until jar is clean and smell-free.