to add (to); to add on; to append
to extend (e.g. a house); to add to (e.g. coals to a fire)
to buy more (of something)
to take care of some business; to go on an errand; to relieve oneself; to do one's business; to go to the toilet
to top up (drinks, water, rice, etc.); to replenish
adding a superfluous "re" to the potential form of a godan verb