OMSP = One More Slot Package/Place
The package/place choice depends on who you’re talking with.
The point of these hacks–if that’s what you want to call them–is they allow you to have at least one other place [slot] on a surface…any surface. If it’s in your game, there’s a good chance you’ll be able to find a OMSP made so you can add something on top of that surface.
Good examples are: more slots on tables, putting stuff on beds and putting stuff on cars.
Keep in mind that sometimes objects become unusable if you’re placing objects on surfaces that aren’t supposed to function as a surface.
The OMSP I use the most is Orange Mittens’s which you can download from Mod the Sims.
This is what it will look like when you get it:
Slide the column where you need it and put your object on top. Easy as pie.