You should invest it into grinding nodes since the higher the node of an area is the higher the droprate of the mobs associated with it is.

If you have extra energy you don't want to waste or don't have time to use, you can go to Alustin and make energy potions from them or if you have an alt, level up Gathering by AFK gathering water with empty bottles

You can also gather with those energy, and if you feel like it you can go to cauldrons and other misc loot places to get a 5% EXP scroll (if you're lucky). This is particularly useful when you want to stock up on them for late-game grinding.

Lastly, i would recommend that you use energy with Patrigio the night vendor when there are 1/2 off energy events like what's happening right now :)

Also if you want to make it easier to get amity with NPCs in a town you can always level a town up.

just adding this one here, you can milk cows, milk is always nice money and does not take long to drain the energy with the minigame, can also activate a gq while you are at it to get some extra money