How much can a surprised character do?

Question

When a character is surprised, they can't move or take actions (including bonus actions) on their first turn, and they can't use a reaction until the end of their first turn.

Well and good.

But can a surprised character still do all those other things listed as "other activities on your turn"? Can they communicate with 'utterances and gestures', interact with objects, and so on? Can they, for example, draw weapons and shout 'help help!', or ring a bell they have in-hand?

In context: The rogue and warlock, who are both very stealthy, try to ambush a couple of guards and "take them out commando-style" before they can raise the alarm. Apparently, in order to do this, they have to not only gain surprise (not a problem), but also roll high enough initiative that they can attack before the guards get their first turn (risky) during which the guards can only, apparently, shout for help and ring their alarm bells. But if it's just about who gets the top initiative slots, what's the difference between using all that stealth, and having the whole party just charge right in and hope two of them roll a high enough initiative to take both guards out before they can react?

Answer 1

No. You cannot move, attack, draw a weapon, or interact with an object while you are surprised.

First (for those more familiar with other editions), in 5e there is no surprise round. Instead, it is possible for some members of either side to be Surprised:

Any character or monster that doesn’t notice a threat is surprised at the start of the encounter....
A member of a group can be surprised even if the other members aren’t.

These are the penalties for being Surprised:

If you’re surprised, you can’t move or take an action on your first turn of the combat, and you can’t take a reaction until that turn ends.

If you are Surprised, you certainly can't move or draw a weapon or interact with an object. Note that drawing weapons and object interaction is only free (first time in a turn) as part of a move or an action. So after your first turn, you will only be able to make opportunity attacks with weapons in hand at the start of combat or with your unarmed attack or an improvised weapon in your hand (or with a spell if you have the War Caster feat, etc.).

Narratively, it doesn't make sense for you to react before you have noticed anything. I feel like this should prevent characters from shouting about the fight until they notice it has started. The first time they are aware of another enemy, they could shout something. However, there is no way to remove the Surprised condition from an ally (short of a Wish), so you won't be able to use your Action (if you weren't Surprised) to save an ally's turn.

The fact that there are many abilities, spells, etc. that prevent a certain character from being Surprised is not relevant to dealing with characters that are Surprised. Also, the fact that 7th level Barbarians can use their Feral Instinct (PHB 49) to act normally is just a case of Specific Beats General (PHB 7); if they go into a rage, they can ignore the penalties for Surprise.

(Unless annotated, this all comes from PHB 189 & 190.)

Answer 2

A surprised creature can do very little. (but not nothing.)

Surprised Condition (PHB 189) :

If you're surprised, you can't move or take an action on your first turn of the combat, and you can't take a reaction until that turn ends.

So what other activities can you do on your surprised turn?

Other Activity on Your Turn (PHB 190)

YES: Your turn can include a variety of flourishes that require neither your action nor your move. You can communicate however you are able, through brief utterances and gestures, as you take your turn.

NO: You can also interact with one object or feature of the environment for free, during either your move or your action.

NOTE: The DM might require you to use an action for any of these activities when it needs special care or when it presents an unusual obstacle. (If you wanted to tell your life story during combat under communicating for example.)

Also note as part of the Specific Beats General (PHB 7) rule;

[...]many racial traits, class features, spells, magic items, monster abilities, and other game elements break the general rules in some way, creating an exception to how the rest of the game works. Remember this: lf a specific rule contradicts a general rule, the specific rule wins.