Fishing is a very solid way for new players to make money. You get crates, can sell the fish you get, ect. If you can get the "Legacy of Chuck" fishing rod that would be a good start, since its pretty OP. People sell it for under 50k typically.
Also, start making a beetroot and cane farm. Although cane isn't the most efficient to sell, its important to harvest cane to get your mcmmo herb up, which will help in the long run.
Besides that, sell your keys to players shops. People buy for like 7.5-8k each, so you can make a lot if your online a while.
Muling also makes decent cash, and can help you get started with supply.