Kitchen bowls/pans/etc (though one of the Exception items is a really cool apple corer-peeler-slicer thing that can be in the back of a cabinet for months but I'll never forget it during apple-baking season)
FOOD IN THE FRIDGE is the worst (food in the pantry not much better)
Flavours of liquor, if I don't have them all out in the open on the bar-buffet
Oh hey let me look in the drawers of my desk RIGHT NOW and list semi-useful stuff I forgot was there:
Whiteboard markers
Business envelopes
A backup hard drive
Most of a ream of printer paper
A pair of thin knit gloves that I've used in the past to type when the room was cold but I haven't seen or thought about in years
A small wad of foreign money from two trips ago that actually would have been useful on my last trip abroad
A supply of staples
...that's not an exhaustive list. And it'd be longer, except three of the eight drawers are empty because I try not to keep stuff in drawers, because I'll forget about them.
I can have things that get "put away" i.e. in a container/cabinet/drawer/room IF that container will be something that I open and access at least every other day. Otherwise, things that get put away out of sight are GONE until I accidentally stumble across them years later.
Limited exception: if there is a tool or device or something that is so uniquely suited for a task that when presented with a task where it would be useful I will immediately think of the tool—and thus remember that I have it—I can safely store it away, as long as the place I'll put it is the first place that I'd look for it.