Good ideas
Use a 6" or longer section of vaccum/fuel hose to start a spark plug. You'll never cross thread a head again and it makes it easy to get to those nearly impossible to get at plugs.
If you've got to start a hexhead screw and the driver is worn to where the screw falls out just before you can get it started, tear a small piece of paper and place it over the nutdriver then press the hexnut into the paper into the socket, the paper will hold it tight. Works for phillips also....
Easy way to clean off heavy corrosion on top attach battery terminals is to pour some Coca-cola (or Pepsi etc) over the terminal, walk away and get your air compressor air sprayer then come back and spray the battery/area off with air, it'll be clean enough to work on then

(I keep an old flat bottle of Coke in the shop frig just for this purpose.
Need a cheap voltage/current tester? Solder 2 wires to a std 1156 auto lamp, one to the caseing and the other to the soldered nipple on the end.
Series it in to the suspected circuit to see if current is flowing (especially handy in troubleshooting battery drain) it'll light up if current flow is present. Or place one end on a good circuit ground and the other where you hope to find voltage, it'll glow if it's there.
A cheapo continuity meter can be made with the above lamp tester and a 12v battery charger/ power supply set on it's lowest power setting. Circuits, fuses etc can be checked. Don't use this on circuits with CPU's, MCU's etc as it could damage them.
One of the handiest tools I have is a pr of 13" channel locks that'll open to at least 5". They make a handy universal oil/hydro filter wrench and disc brake caliper piston depresser. It's never met a filter it couldn't get off
Volfandt