Good creatures to kill to obtain bones are low-level ones in game
Newbie Money-making Tips: When first starting out Runescape, knight gold-making may be a hard and difficult task.
However, there are many significant ways to start your cash flow, although I would recommend later on that you get yourself a money-making skill that you can depend on for a good income (mining, fishing, etc.).
You can try collecting regular bones and selling them to players who level up their prayer skill. Bones are cheap, and they aren’t very hard to get either. Regular bones (the kind that nearly every creatures drop) are worth around 25gps.
Good creatures to kill to obtain bones are low-level ones (goblins, rats, chickens, etc.). Advertise your merchandise in a major town and also be sure to list the selling price for each bone (i.e. “selling regular bones, 25gps each”).
Bones are plenty easy to get and a player collecting regular bones to sell them can make 7.5k-10k per hour.
If you are ready to quit or retire from the game for awhile and have leftover money to spend, then I highly suggest you invest in some type of discontinued item, be it a Santa hat, Halloween masks, or even party hats.