Spoiler
While you play adom store each level you have visited (except ID levels) in a seperate file in your .../adom/adom_dat/tempdat/ folder, with names like "adtl04_1", "adtl05_1" and so on. Each file represent a dungeon level complete with all items, monsetsr and dungeon features (such as special one-shot room effects).

To abuse this feature simply tell your OS to sort the files after theyr date, now the last level you left will be at the top (or bottom, depending on sort mode) of the list. So simply drop the items you want to duplicate, leave the level, make a backup of the apropriate file, enter the level, puck up your stuff (and do whatever else you want to), leave the level again, copy your backup file back into the tempdat folder, overwriting the new one that just got created, enter the level again, and everything will be back like it was when you backed up the file. All the items you just picked up will be back on the floor for you to pick up again, all monsters and dungeon features are also back the way they where and so on...

In other words you can go back and pick up the same item, kill the same monster or benefit from the same room as many times as you like, just keep leaving the level and overwrite the updated temp file with the one you backed up before you picked up or killed the stuff you want to duplicate.

I also noticed that you can "switch off" wilderness encounters by replacing the wilderness temp file with another one (just re-name some other file and overwrite the original). Keep a back up of the original if you want to switch them back on though...