If you suspect hostiles on the opposite side of a closed door, and you haven't engaged in combat against them, you can enter combat, open the door, and move to the side out of LoS and then end combat. Useful if you don't want to have a 25 AP cost applied to you at the start of battle for opening that door.
The lantern belt item can be activated to stop the dopplegangers from appearing on Forbidden Isle while its light holds up.
The thugs in the GMS compound do not have a key to get into the gun turret control room. You can enter that room, shut/lock the door in combat and then, once it ends, activate the turret outside which should kill at least two of them as they walk back into the cafeteria.
You can charge items placed on your hot bar instead of finding them in your inventory. For that matter you can hotbar repair kits for easier repairs on equipment, instead of switching between tabs.
You can export/import a character to earn oddity experience again from quests you complete. Oddity items found will not grant any more points obviously.
Marsh Honey increases your perception by 2. The Juice by 1. Mushroom Salad by 1. Googles can be found to grant you another 1. All of this can get you +5 to perception for 50 seconds if you're looking to reveal some secrets.
On that note rathound barbeque, the Power Fist, Rat Hound Armor, and Adren shots can grant you +5 strength for 15 seconds. Useful to push some blocks or boulders around. I believe (I can't recall) a certain unique armor found in the jetski dungeon can grant you +3 strength when it's powered and activated, allowing for +7 strength for 15 seconds.