So as standard, everyone has one thing they can do with a Reaction - they can use an opportunity attack if there is a trigger. They could also create a trigger of their own with the Ready action.
I have been allowing a couple of extra things that my players can spend their reaction on:
How do people feel about these? The former one in particular has been fun with the group I've tried it on. There's always been some off-turn chat, and giving them a resource they can use to justify it makes for some interesting decisions (and has actually cut down on subconscious metagaming1). I don't think it would work with every group, though.
Is there anything else that you have allowed that's light enough? Without a Ready action and a trigger, I personally wouldn't allow anything that looked at all like an action, a move or anything that requires finesse (so using an object or moving a bit are out).
1 It's very easy to just let some words slip, and very difficult not to take the words of someone else into account when you take your own turn. Putting a cost on those slips of the tongue gives people more of an incentive to avoid them.
I have been allowing a couple of extra things that my players can spend their reaction on:
- Talking outside their own turn. Specifically, I allow anyone to spend a reaction to speak a short message of 12 words or so once. If they realise they should have warned people about something else? Tough. They already used their reaction.
- Dropping an item they are holding. Not placing it anywhere, just dropping it. Obviously this doesn't negate the damage effects of things like Heat Metal, since the damage for that is dealt on-turn with a bonus action.
How do people feel about these? The former one in particular has been fun with the group I've tried it on. There's always been some off-turn chat, and giving them a resource they can use to justify it makes for some interesting decisions (and has actually cut down on subconscious metagaming1). I don't think it would work with every group, though.
Is there anything else that you have allowed that's light enough? Without a Ready action and a trigger, I personally wouldn't allow anything that looked at all like an action, a move or anything that requires finesse (so using an object or moving a bit are out).
1 It's very easy to just let some words slip, and very difficult not to take the words of someone else into account when you take your own turn. Putting a cost on those slips of the tongue gives people more of an incentive to avoid them.