Tools to your level of ability while on the road. Does no good to have all the tools to change out a ball joint if you can not do it along the road or in a campsite. That goes for the mechanical parts.
As for the interior/house side, get yourself a cheap pex crimp tool and some rings to go with it. Grab a couple different elbows and straight joints and maybe even a few sharkbites for hard to reach areas. Add a couple 3 foot pieces of blue and red pex. Some eternabond tape and a tube of dicor/caulking gun.
And a credit card for the hard stuff.