The first one of these you have to shoot to destroy, the second you use an access card, and the third you use the cloaking device.
Lava
Oh noes!! Red liquid!!!! omgwtfbbq!!!1!!111one!11!!1
Napalm Bombs
Often contained in red boxes, these annoying bombs spray fire on both sides when they go off. If Duke walks behind a red box, it has a napalm bomb, otherwise it has food.
Pounder
Bang bang chitty chitty bang bang, our fine four-fendered friend!
Rocket Launcher
How does this thing know where you are?
Spikes
I'd think if Duke impaled his foot even once that might stop him from walking...but he IS a self-proclaimed hero.
Spinning Turret Gun
The most annoying little peckers in the entire game. You can only destroy these with a weapon other than your normal piece of crap.
Toxic Waste
Stored in barrels, shoot these from a safe distance.