Buckles for your fins and prestrap the finstrap into it too. Otherwise you'll be sitting out that dive because it takes a while to thread the strap into the buckle.

Also, in their haste to get me onto the boat, the DM undid the buckle & lost it. So the extra buckle is a dive-saver.

Even if you have spring straps, get the extra buckles, b/c they can and will come off.