Any decent IFAK is going to be too big to carry in the belt.
I'm using a Condor rip away IFAK
When you start filling it up it takes a lot of space.
I like Nola's IFAK contents, the israeli bandage is fantastic.
A point that often is forgotten is that we should carry the tourniquet outside the IFAK pouch because it needs to be readily accessible, I'm guilty of this one too...
You need to remember to carry surgical gloves, multiple 2" gauze rolls and a nasofaringeal airway.
You can add hydration salts an a big syringe with an irrigation cup.
I'll rather make my own kit that buying a pre made one, and above all you need to learn how to use
the IFAK contents and practice often, PHTLS book is a good source of information about first aid.