kellymom.com :: How much expressed milk will my baby need?
That's a good link to check out about how much milk a baby needs. The average amount of breastmilk a baby takes in over 24 hours is about 25oz, so a general place to start from is about 1oz per hour you'll be away from your baby.
My daughter likes to eat frequently so I sent 4 bottles with 3oz each (I was away from her 11 hours, 7am-6pm). Sometimes my MIL would even divide them smaller so she could have them more frequently. Every baby is different though. Now that she is older, recently I cut back her milk from 12oz to 9-11oz over 3 bottles instead of 4.
I send her milk in the bottles, usually fresh milk I pumped at work the day before. Every once in a while I add some frozen milk in there and freeze some of the fresh to rotate my freezer stash. It saves on bags that way and I figure fresher milk is better since it is made for her specific needs at the moment and hasn't (possibly) lost any good properties with the freezing and thawing process.
The way I do my mornings is I leave her sleeping (as long as she is still asleep) til just before we leave. The last thing I do is wake her, change/dress her, and nurse her. Then I don't have to entertain her while trying to get myself together for the day.