Even starts? (I need to dump some milk before vaca)
Unless your ‘starts’ have two or more ADULT leaves, then, no. Seedlings don’t need fertilizing until then.
Can you put the milk in the freezer while you are gone? Milk freezes just fine; no need to waste it.
BUT - if you have to dump it, water it down and feed it to any potted plants you have, inside or out. Also, give it to any flowering shrub in the yard. :)