Well if I empty out my tool bag
The basic stuff we need are
3 pairs of good quality grips,standard pipe grips
A cheap set of screw drivers with various philips,posy and sloted in
One slotted average size screw driver that you can abuse for many purposes,may get one in set
1 good long philips screw driver
Tape measure
Boat level
Standard Hammer and brick+ wood chisel
Allen keys and maybe security key set
Tap spanner as said
stanly/craft knife
junior axe saw,pipe slices,normal axe saw,do not forget blades
adjustable spanner (I have never used mine,corrodes up first)
Foot prints(again I never use as log as you get good quality pipe grips)
Immersion heater spanner
plier set,with pliers,lond nose pliers and wire cutters
Then you want your jointing compounds,ptfe tape,standard washers for taps,ball valves,silicon greese
Then,in the bottom of the tool bag, to weigh it down a bit and stop any one running off with all your tools, you need bits of pipe ends ,nuts and old olives,maybe the odd old motorized valve body,a few old brass ball valve bodies,a few old solvent weld brushes,about 3 dozen rusty screws and a few crumpled up copies of shower screen instructions,right at the bottom