On page B24 it gives five things in order to resolve
- Morale check
- Movement, except if you start in melee special rules applies (explained later) and you forfeit casting spells if you move
- Missile Combat
- Casting Spells
It doesn't make note of arming oneself. If you look at the section at using oil or holy water they both don't make mention of readying the item. It seems the assumption that within 10 seconds it just happens
On page B47 it notes that using a magic, except for weapons, armor, and protective devices, require concentration. While it could have been written clearer it probably means that using a magic item is the same as casting a spell. I.E. using a magic item is the only thing you can do in that round. This seems to apply to scrolls and potions as well.
With the exception of magic items and spells, you could generally abstract the above sequence into allowing the character to move and do one significant and time consuming action. Or to abstract it further the character can do two actions but only one of those actions can be an attack and only one of the actions can be a movement. So you can move and attack, but not move and move, or attack and attack. Casting spells and using magic items consume two actions.