I am now a co owner of RustyMC! so I will be talking to billz about adding these to the server, here's my ideas:
shop sell and money system - add money and shop and sell and auction house like all servers
clans - make clans with friends and have clan wars
crates - f2p crates that you can buy crate keys with maybe a exclusive currency
shards - exclusive currency to buy spawners and crate keys
custom fishing system like a lot of servers have with fish crate maybe
I'll ask billz!