For 3 feeds I would do at least 1 full pumping session so you're telling your body to keep making milk (this is dependent though on if baby is 6 weeks or 11 months old!) No need to pump and dump!
Baby will be 2.5 months old. I also plan to nurse right before I leave her and it should be 2 feeds I am missing but could be 3 if she eats earlier then the 3 hour mark at some point during the day.
Yes, I would do at least one full pump....maybe two. I agree that you probably don't need to dump unless you get completely smashed. Otherwise, it's fine to feed to baby. Or if you have absolutely no way to store the milk at the right temp and bring it back (but generally speaking, even for three feedings, the milk will probably be okay at room temp...I think it's 8 hours?)
If baby will only be 2.5 months old, I would try and pump every time that she eats - so 2 or 3 times. If she was older I'd say 1 good pump would be sufficient, but at that age I'd be wary of skipping feeds/pumps.
I wouldnt do a full pump if you have a good supply already and it is just one day. Unless you get clogged ducts as someone already said. Just pump enough to not be too engorged and leaky. If it were me I would just take my hand pump.