[@Fading Memory] I have an idea for that.

What I like to do as a player when combat comes around on forums, is to list out my turn as...

Movement:
Action:
Bonus Action:
Reaction:

That way, if you do have a reaction, you can make note and let the DM know ahead of time that if the opportunity arises, you can use your reaction.

The only downside to this would be if you decide to use Shield as your reaction, you can't change your mind and pick a different reaction spell.

How does this sound?