DnD 5e has a fairly clear set of rules governing a player's possible Actions in Combat, and in other fast-paced situations a GM may break time into rounds. Among the listed actions, some would seem to initiate combat (e.g., Attack) but others are routinely performed out of combat (e.g., casting a ritual spell).
Certain rules make the combat actions sound like they are only for the purpose of managing fast-paced events. On the other hand, there are inconsistenties with this view. For example, spells cast as bonus actions are especially fast spells (citation needed), but cannot be cast as an action (citation needed), so length of time cannot be the only distinguishing characteristic between spells which can be cast as an action or bonus action.
So ... what can a player do in combat that they cannot do while adventuring?
Here's the start of an answer (to which I'll add as answers come in):
- Behaviors that trigger combat. (Debatable, since the behavior may have actually occurred out of combat.)
- Certain reactions whose triggers cannot occur out of combat.
Please clearly specify your reasons for your answer (e.g., RAW, RAI, logical deduction, common practice for groups you've been part of, etc). Citation of rules or expert opinion adds value to your answers.