I've found arrowheads, one really cool one, a few very old cartridge cases and a really rusted out trap. Found a few iron wagon wheel 'tires' on the prairie and shovel so old that the metal was almost all rust-colored dirt as I was trying to free it from some frozen dirt. A very small cast iron wood stove in the middle of nowhere in Eastern MT.
How about "almost" coolest thing? Here's one:
Was about 2 miles off and 1300' above a logging road, no trails in the area, in South Central Montana and came across a small, say 8'x8' with short sides, fallen in and almost flattened, log cabin looking structure placed on a rounded, not 'knife edge', ridge. Moss and grass had grown through most of the logs, all small diameter, and you could see the ridge pole and the poles that framed the very-short door. Some logs were pretty solid, others on their way to compost, all cut with an axe, not a saw blade. This got me thinking that this was made prior to saws being in everyone's backpack! Who makes cabins, even small ones, with an axe?!? I'm like "I found a trapper's cabin!!" and had images of Jeremiah Johnson-ish dude living there, that I'd find a cache and a bunch of cool trapper stuff under the wreck of the cabin, probably some amazing and perfectly preserved journal and obviously his gold dust stored in a tanned bull elk nut sack.
I was carefully moving a few of the poles, amateur archeologist-style, and taking a few pictures and I see some black, shiny material - that turned out to be thick black plastic film of some kind. Like heavy duty garbage bag stuff but a bit thicker. All my dreams faded, no documentary, no gold dust. Then I saw more and more of the black plastic under blow downs and grass humps in the surrounding approx. 50 yard radius. Not sure when plastic film was invented, but not that long ago. It looked like the cabin may have been lined with it from where it was underneath all the logs.
The cabin clearly took a bit of work and was someone's camp and I definitely dug around looking for treasures, but found nothing. I'm always looking and it's fun finding stuff out in the wild.