I'm not very good with conventional DIY, so I'd say my attempts border on the experimental rather than the innovative. If there's anything majorly wrong with something (plumbing or electricity, for example) I get someone else to do it.
DIY Pen-Lid Repair
I usually write with fountain-pens, and after a while, you find that the lids stop clicking into place and start falling off in your bag. This is particularly annoying as you then get ink everywhere, and can damage the nib. Solution: Line the rim of the lid with blu-tac. It stays put, which is great, for anyone who knows the frustration of having to 'wear in' a new fountain-pen nib.
Talking of wearing things in...
How To Wear In New Boots
I ended up with far too many socks at one point, and when I bought a new pair of Doc Marten boots, I (naturally) kept getting blisters.
I cut up a thick pair of socks, just keeping the end with the elastic on, and wore them (elastic-side around the bottom of my foot rather than my ankle) on top of my normal socks.
My boots stopped rubbing, and I didn't have that awful two-pairs-of-socks feeling wear your toes get trapped and your entire boot feels too tight.
DIY Shower-Cap
This sounds a bit silly, but when I had a shower without a detachable shower-head, I used to tie my hair up and stick a small plastic bag over my head. I thought this was ingenious, seeing as the handles made ear-holes (embarrassing picture coming up!):
