Buying feather packs - 200-230K/H
Grinding chocolate bars - 100K-150K/H
Tanning hard leather - 120K/H
Filling water containers - 110K/H
Buying ale from the Rising Sun Inn - 50K/H
Buying kebabs in Al Kharid - 35K/H
Picking potatoes - 30K/H
Just a few ideas from the f2p money making osrs wiki page.