Fluid Film is probably one of the best anti-rust treatments, as long as you don't mind that it's a bit sticky and smells of sheep.
Back in my gun days I did some research on the best rust preventative and found a guy who did a fairly large scale test and Eezox came out on top, as I recall. It's very thin, like WD-40, but doesn't smell great either.
For that matter, WD-40 makes a product for long term rust prevention. Supposed to last a full year.
In the end, what most said about an oily rag is probably the easiest and should work just fine.
And #0000 steel wool (with oil) is great for removing surface rust on guns, without damaging the bluing. Should work fine on a prybar.