Would those be specialized kits or a universal one? Different things get repaired differently.
This could be done very simply with the usniversal kit.
Or very complicated:
~ armour
+ leather
- small repairs/taking care (e.g. from 35 to 50) - oil or lard to take care of the leather that's been hurt a bit
- bigger repairs (e.g. from 0 to 35) - needle set and string
+ chainmail
- small repairs/taking care (e.g. from 40 to 50) - rough cloth and oil to clean the material and prevent rust
- bigger repairs (e.g. from 0 to 40) - erm ...good luck without a bit amount of white or blacksmithing skill?? (would mean you'd have to watch out better for your chainmail and take care of it while it's just slight damage to make it worth repairing)
~ weapons
+ swords, daggers, axes (and other blades)
- small repairs/taking care (e.g. from 40 to 50) - rough cloth and oil to clean the material and prevent rust and fine sanding stone to sharpen it better
- medium repairs (e.g. from 20 to 40) - several sanding stones to sharpen it from bluntness
- big repairs (e.g. from 0 to 20) - blacksmithing skill and equipment
+ hammers and similar
- small repairs/taking care (e.g. from 35 to 50) - rough cloth and oil to clean the material and prevent rust
- bigger repairs (e.g. from 0 to 35) - erm ...no idea ...really o_O ...blacksmith?
...and as you see some of these items (cloth, rock) don't wear out as fast as others (oil).
Maybe the player could buy a box "repair kit" and then fill it up with the utencils he/she needs for his/her needs. And he/she runs out of a certain piece of the repairing equipment, the player just buys only a new piece of that (and not the whole kit).