This isn't really any one particular project, but this is MUST HAVE for any quick turn low-buck projects: Instamorph (Polycaprolactone), or shapelock, friendly plastic - there are a number of brands. It is a non-toxic plastic that you can form yourself by hand. Simply place it in hot (NOT boiling) water for a few minutes and once it turns from white to clear just shape the plastic any way you want.
Need a wrench you don't have? Well, form a diy wrench in-place over the fitting with instamorph.
Google it, it's pretty amazing stuff. You can tap it and drill it (slowly), but sanding doesn't work well (it heats up and gets soft). Since you tend to form it by hand the results often don't look very good, but it is functional.
I haven't used it for much more than making a little holder to keep a specific allen wrench near a fitting that needs it often. However, it's the kind of thing I'm glad I keep on the boat in case I need something when underway and Lowes or West Marine is unreachable.
The following pics are from the web to give you an idea of what it can be use for in a pinch.