Hyper-Compressed Ocean if you are into fishing.
Wormhole Generator: Shadowlands to get around SL easier. All you need to do is learn SL engineering and it works at any level.
Get plenty of
Straddling Jewel Doublet and
Revitalizing Jewel Doublet while you have AH access for current and future chars. Especially the second since you can't get the rep to craft it at 20.
Get a multi-person mount like
Traveler's Tundra Mammoth so you have an on demand vendor and repairs if you need it. Be sure to buy with a goblin because they will get the faction discount and save 4000 gold. If you end up being rich or buy a token you can consider
Grand Expedition Yak for 120k gold.
Finish the Dragonflight campaign up through
Moving On. This will enable adventure mode for your alts. In the prepatch this will let all four main zones scale to 10, so they will be doable with any alts.
Unlock the warband bank in the prepatch. If you want to store a bunch of stuff in there get at least the second tab at 25k gold. Make sure you leave all your gold on a character you will have access to once your sub ends. You can put it in the warbank, but you never know if something you want later will pop up on a vendor. With the gold cap you wont be able to get it out, so leaving it there should be fine in the long run.
The exploration maps are handy, but I think warbands will enable everyone to have access to all discovered flightpaths. So get all of the flightpaths on a character.
Get materials for any professions you want to level while you have access to the auction house.
Unlock Mechagon if you want to do stuff there in the future.
