It's usually dark when I get to my boat. After climbing down the ladder and feeling around the breaker panel for the cabin lights a few times I came up with this $6 tap light from Lowes. So far I've only replaced the batteries once after two years. I also put them in my cockpit lockers to make it easier to find things in the dark.
When I get aboard and it's time to cook dinner I found I didn't have enough light in the galley, so I put this $19 LED light I found at Bed, Bath & Beyond above the range
And two of these LED touch lights ($8) under the shelf that hangs from the cabin top over my galley sink, so I can see to wash dishes.
Everything uses batteries so there were no wires to run or splice. I used some heavy duty velcro to stick them in place, so I can undo them later if I want. A little Goof Off and you'll never know they were there.
It's not the sexiest project I've done but for under $40 these lights get used every time I'm on board.