I carry lots of tools. They add weight but as a full timer I don't have a shop back home to go to when I have a project to do.
All my tools are placed on the left side of the trailer where my dump valves and other " trailer business" type stuff is. I carry a two drawer tool box in my rig. This is also where I keep the wrench for lowering the rear stabilizers and the one for lowering the spare tire and so on.
Inside my tool box I have a large assortment of adjustable wrenches, a 3/8drive socket set, vehicle and household multi-testers, cutting tools, screwdrivers, and so on. I also carry a small Dremel tool set, a battery charger, and one of those Black and Decker battery powered kits that includes a drill, saw and other tools. I have a small block plane, dovetail saw, and a little handsaw with four changeable blades. I haven't seen one of these for sale in years and don't know if you can even get them anymore but mine is really handy. Because I occasionally modify some of the features of my trailer, I also carry a hole saw kit for when I need to knock a hole in the side of my rig for another accessory or something. (See a previous post about make the rig suit your needs.)
A couple of other essential items for me include my 18 gauge DeWalt Brad Nailer and a small Campbell air compressor. The brad nailer is the same size the factory uses to tack trim and a lot of other parts of your rig together and I often state I could rebuild my rig with mine if I had to.
I have several large Rubber Maid tubs that I store other stuff in. One contains all my spare sewer hose and connectors. Another holds all the extra electronic items I might need like television cables, junction boxes, switches, and so on. Two other large tubs hold caulking and sealers that I use for emergency leak repair, and other misc. items that I might need and usually do. One final tub holds all the various cans of cleaner, lubricant, paint, polish, soap, and stuff for washing the truck and trailer and providing maintenance as needed.
I have one small plastic container with all the fresh water connectors and what not too. It's just large enough to put a couple of new water filter cartridges in for use later.
That's about the size of it. I can fix my roof, make minor repairs to my truck, build small things out of wood, and generally handle about anything that comes along if I have to. Owning and living in an RV full time isn't much different than owning a house. You still need to be able to make repairs or do maintenance from time to time. Some folks can afford to pay someone else to work on their rig. I prefer to do it myself unless it's beyond my ability.