It is absolutely true that you can drop skydivers and tow gliders with a PPL to get free flying!
I've dropped lots of skydivers. Initially it was unpaid on a PPL although I eventually got a CPL, moved onto bigger aircraft and then got paid for it.
Dropping jumpers is GREAT fun, is a fantastic way of keeping current, does wonders for your aircraft handling skills and in my case was a fun way of getting enough hours to get a flying job.
To drop jumpers in the UK you will need to get a British Parachute Association Jump Pilot's ticket. You can find out how to go about getting qualified by reading Section 9 of the BPA Ops Manual available
here.
There will be someone on here who can advise you on how to get involved in towing gliders - I've never done that
The one thing that I would say is that you mention 'expenses' in your post and if you've only got a PPL, expenses are very dodgy ground. When I was dropping jumpers on a PPL, most places I flew at picked up my food tab at the drop zone canteen on the days that I flew there. Although on a busy, eight hour, flying day I could sometimes eat almost my own body weight in toasted sandwiches (it's hungry work!
) - no money ever changed hands and I would advise very strongly that it shouldn't.