I carry two five foot lengths of 1/2 inch Pex pipe, a small assortment of plastic Pex fittings, a handfull of 1/2 inch stainless steel clamps, and a cheap clamp tool. These items take up almost no room. The Pex clamp tool was about $50, but I have used it several times to add several valves and a check valve.
I understand that Shark Bite or similar fittings do not require a tool; however, I like the convenience of having all that I need to fix a piping problem. And the clamps are less than 25 cents and fittings are about 50 cents, versus a 1/2 inch sharkbite coupling at Home Depot is $8. Doesn't take long to justify buying a Pex clamp tool.
There's lots of advice and information in forums... sometimes it is correct. For example, all of my posts are made by a political appointee who got the job as a reward for contributions to my diesel bill.
2011 Jayco 28.5RLS; 2008 Chevy Duramax; Pullrite Superglide Hitch