I've even used one of those cheap telescopic fibreglass flag poles (just not used the very thin top section 'cos it waves about too much). If the ground takes it, I hold it up using one of those screw-in washing line things - a metal one can be used as an earth as well
I made some pole sections from a load of 22mm PVC pipe and a handful of straight connectors. If you cut four lengths of pipe to about 50 cm and solvent weld a Tee piece to one you use as a top you just slot them together. Then tie the top of the slim jim to the tee and use a bit of lace to hold it in place at the top you get quite a serviceable mast for about £7.
I used the 22mm pipe because when you wrap it in fabric tape it's just the right size to slot into molle. I can send a picture if that helps explain it.
I mean you can hang the slim jim antenna of anything non-metal, so it doesn't have to be up a pole, it's just that when I activate and chase SOTA I want as much height as I can get. I know people hang it out windows and such and any tree-branch would probably do too.
Another interesting option is the flower pot antenna. I've been tempted to try that out, but I'd need to get some suitable pipe first.