Originally Posted by Shishkebab
when you hold ALT it will show the barrels, crates, corpses to loot and so on

This is easy, but there's a bug where properly set-up objects won't display tooltips. This bug affects items like Rope and Playing Cards.

Basically, what you need to do is go through all your desired Root Templates and set their Tooltip Type to WorldAndHover.

Originally Posted by Shishkebab
I want to make it toggle, so instead of having to hold ALT the whole time, you could just press ALT do turn it on and ALT again to turn it off.

You don't want to keep ALT on. Holding ALT while looting delays the rate at which you pick up items.