Torch light, spare batteries. Live musician if possible. Bow Saw - very useful if houseboat happens to get tangled in any troublesome branches etc. Fishing Tackle and bait. Gardening gloves or similar, for handling wet ropes and anchor etc.
Wet ropes are very rough on unprotected skin.
Playing cards, 'Trivia Pursuit', 'Scrabble', Backgammon, Chess etc., as required. Warm clothing for evenings under the stars. Particularly for persons with impaired circulation. They're mostly barrel-shaped, similar in height to domestic toilets but 'fatter' around the 'waist' . Anyone who can walk can use them the same as they use an ordinary domestic toilet.