On Rhapsody I may err on the side of conservative to be able to fix stuff. I have everyday onboard tools / parts and extra stuff I take when cruising.

Here is what I consider essential to have:
  • Screw drivers - 2 flat head and 2 phillips head (small & large)
  • Adjustable end wrench medium 8"
  • Sharp knife
  • socket wrench set both SAE and metric (I think it's ~ 25 piece set with ratchet and extensions) - Yanmar has both standards
  • roll of duct tape for emergency repair
  • a bunch of ty-wraps
  • small tube of sealant & epoxy for emergency repairs
  • Leatherman multi-tool (cutters, needle nose pliers, file)
Check this page and download the excel spreadsheet "Recommended Onboard Engine Spares with Part Numbers (Excel Spreadsheet)"

My guess is there is less than 8 pounds of stuff stored low in the boat.