Your repair kit contents will vary depending on your level of equipment repair expertise. At a minimum you should have:
1 mask strap
1 fin strap
1 snorkel keeper (they are useful for lots of things besides keeping snorkels
)
a couple of spare ss clips
assorted zipties
a small o-ring kit that includes tank valve o-rings and portplug/hose end o-rings
1 brass o-ring pick
1 set of thin wrenches like
these
1 small adjustable wrench
1 small screwdriver with multiple tips
1 pair of needle nose pliers
1 pair of emt scissors (can be used to cut all kinds of things including zipties)
1 small set of hex/allen wrenches
1 small tube of aquaseal
1 piece of cave line (nylon string)
1 piece of bungee (1/8" or 3/16")
duct tape (a couple of feet wound around a pencil)
1 roll of self-fusing silicone tape like
this
With this stuff you can fix almost anything. You can fit all of this into a hard plastic pencil box and keep it in your dive bag.