There are items and powers in 4th edition that allow you to spend a minor action to have an effect until the end of the encounter.
- An armor with a daily minor-action power that grants it a +2 bonus to AC
- A power that gives you +2 to all defenses until end of encounter
Suppose you are in front of a door and you know there are monsters on the other side. Can you use these minor actions to active the buffs before initiative is rolled (even before the surprise round)?