My sacs tomahawk s590 ( not so common brand? ) has quite nice storage space and I have there:
water separator/fuel filter
anchor and rope 40mtrs + 30mtrs
screw drivers, hex-drivers
wrench-set, adjustable wrench
crimpers + connectors, other pliers
prop nut set, extra sockets for prop nut
duck-tape, electrical tape
clamp-seal, electrical pump
immersion suits and life-jackets
and also SPARE PROP. Unfortunately in Finland there is some scrap on the sea at spring time: pieces of wood, empty bottles etc. because when ice is melting away it brings scrap from islands. Also my spare prop is with 2" less pitch if there is a need to take more load on the boat. Ok itīs not fun to change prop on the sea but if you have to you can!
We use my RIB mainly to go to summer house at off-shore island 24km from main land. When going there or coming back with not best weather conditions you want to have spares/tools/spare prop with you...