I have a few ideas how to improve the action-menu and some menus around it.
The use-key could spawn (and close) a little menu in the middle of the screen that is to be controlled either via mouse-cursor or scroll-wheel (which will not open the menu) whenever multiple world-actions are possible. Self-actions could be off-loaded to the inventory, and the squad controls need to have its own menu, simply because of its many options, similar to the inventory. That way the first few numerical keys (and the scroll-wheel) can be used for changing weapons (including put). Objects that have options and are being looked at need to be highlighted somehow.
What needs to be done amongst other things is, to remove the abillity to accidentally "do" something because you either didnt know the menu was open, or you tab the use key numeral times because you're "in a fucking hurry".