Some of the rarer anubias and java fern variaties are in hot demand, as is anything rare!
Swap duckweed for frogbit, dwarf water lettuce or RRF... that will trade for a lot more.
Swap java moss for fissidens, xmas, spikey, weeping, cameroon or flame.... they in high demand
Swap amazon swords for uncommon sword - or crypt - varieties. For my area, red rubin, red flame and tropica swords seem to be in high demand.
Buce are definitely a good one (i have about eight of them, most are brownie, the others are three types, they take longer than anubias to grow out).
Anubias (pretty much large and small ones with nice or interesting shaped leaves like coin/round leaf, pinto doesn't seem to have as much a hold on people right now, but that might resurge into demand), java ferns, water adapted bolbitis (not heteroclita), and most moss (xmas, java, other hard to get a hold of ones like willow).