I've tried everything lying around - fishing line, fishing weights, tennis balls with holes poked through them, dyneema cord... and I still can't get much height. Is it worth it to invest in the real stuff?
Do you think if I just get a bag and fill it with dirt/rocks, that would work just as well as any throw weight?
For me throw line, throw bags and a line cube are essential to tree climbing
I spend enough time pfaffing with throw line, right tool for the task, after trying a few different types of bags I've settled on the Harrison Rocket. They just work, some bags will hit a limb and absorb the energy and fall back to earth. The Rocket however will glance off and keep going. Manipulation seems to be easier, it will roll over branches others pop over sending the bag where I don't want it.
I'm all for making my own gear when I can, if you find a way to make your own bags, I'd be keen to see them.
Oh and having 2 lines and 2 bags is handy if you get one horribly stuck and have to climb up and get it.
You will throw even higher using a 10 oz bag. 8 oz bags are good too if the bark isn't too rough. I prefer the stiffer "slick lines" like "target (neon)" or green "bullseye" line. Use the lighter more limber lines ONLY with a line cube as these lines tangle very easily.
Mono filiment lines with fishing reels are sometimes used out west with Big Shots (sling shot on fiberglass pole) or compound bows. Ranger Rick frowns on bows in the park however.