Buying Bonds through OSRS is a waste of cash merely because you can buy a bond in osrs for 2m which on average is worth 14m RS3 (Depending who's swapping) while the bonds on Rs3 are around 7m. it's cheaper to buy bonds on Rs3 but i personally suggest (Highly recommended) you buy membership us IRL money because it doesn't cost too much and it is at least 1 month of membership also you don't have to spend your hard earned money in RS which you'll most likely need for members to be worth it anyway, but if it comes to your question. Either Cut Yews,Catch Lobster, or Merch using the G.E

for f2p the only thing i can really think of is cut yews. However like the other guy said before it's not really gonna be worth it unless you have the stats to make good money fast as a member by doing like skeletal wyverns or something like that

merchmerchmerch and peekay

Honestly just save some money up and buy membership with real money. It will take awhile to make 2m from scratch.

I have a friend mining and smithing steel bars. It's a bit slow, but turns a decent profit in the end.