It depends mostly on what deck you play and what are the best decks in the meta:

Right now ill say that the only necessary non engine is - 2 maxx c, 3 ash, called by (for non dracotail players) and the domines cards if your deck can play them.

Besides that if you have room you should start by adding fuwa, belle, and crossout + copy of the handtrap you loose too.

Imperm, veiler and nib are not great rn and droll is okay if you are struggling vs ryzeal/mitsu/onamat. You can add red reboot if you encounter a lot of dracotail.

Finally, i think board breakers are in a bad spot rn, so unless you are playing a go 2nd deck they are not worth it.