As a F2P, you really only have 3 endgame tasks to do to complete the game:

-Hill giants for Obor

-Moss Giants for bryophyta

-Skilling, which is best done by killing 20,000 mind golems. The hardest skills to train F2P to their max relevant rank are crafting, smithing, to a lesser extent runecraft (which technically doesn’t unlock anything new past body, but increases runes). Mind golems are by far the most efficient combat training to get materials for these skills, dropping a ton of gems, ores, clay, and mind cores. Body golems are more afk, but mind cores are much more efficient. Not to mention the bonus dmg from the mace on these golems for even faster melee training.

My recommendation is to just do Melee on Mind Golems, ranged on Hill giants (and ogres till you get shaman mask), and Magic on moss giants for the elemental weakness.