I can't tell you what you need, but I can show you what I carry in my go bag. It is pretty rare that I don't have what I need to fix just about anything scuba related on the boat or anywhere for myself, customers, or students.
First is just a generic toolbag. It zips closed and keeps everything from dumping in the car or boat.
This is everything from inside the bag. Starting from top left and working back and forth.
Small tacklebox in a can coozie, Dive Rite tool roll, three shearwater cases, new generic K style inflator, two rolls of paracord, misc bungee, two spare mouthpieces, roll of hockey tape in a ziplock, spare 6" HP hose, blow gun, scissors, lighter, 22" LP hose with QC6 fitting, lighter, zipties, adapter harness from molex to 3.5mm, spare shearwater strap, spare mushroom valve, snorkle keepers, spare QC6 fittings, acid brushes, 4 tubes of e6000, pill bottle of steramine tablets, pack of skabs patches, plastic prybar, bug repellent wipes, cheapy IP gauge.
Next, inside of the cases.
First one is batteries, 9v, AA, AAA, CR2, 123, 2032, and whatever the shearwater transmitter battery is.
Next is spare rebreather cells of various styles, another spare mushroom valve, adapter harnesses to make different cells work in different rebreathers
Next is a few different styles of calibration caps for different rebreathers.
The small tacklebox is Orings on this side, a spare stem, spools, valve wheel spring and nut.
Another package of skabs. These things are amazing, they fix everything from drygloves, to drysuits, to counterlungs, to BC bladders. They are made for side of the trails bicycle tube repairs, but they are amazing and fast.
The other side of the tacklebox is some batteries, port plugs, wingnuts, fin strap bolt, an OPV, Oring picks, and some triglides. This little kit goes everywhere, even if the whole bag can't come, this thing fixes most issues.
Lastly is the tool roll.
From top left across and repeating. the stuff on the top goes in the zipper compartment on right.
K inflator tool, sex bolts, 5/16 wingnut, 3/8 wingnut, tire inflator, tiny tacklebox of port plugs, spools, OPV, DIN and yoke rings, emery board, silicone grease, O2 lube, flush cut dykes, flat screwdriver, Schraeder tool, pick set, two round pin spanners, blowgun with shearwater battery tool, small screwdriver, heavy pick, multi bit screwdriver with bits in the handle, two crescent slimline WideAzz spanners, folding utility knife, allens metric and standard, offset needle nose pliers.
Any questions about what it is or where to get it, just ask.