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stomach nailed it...... but to add....
there are only 3 universal resorts iirc that include the free express pass......so ask when you book..... hard rock/ portafino/ and another one....you will wait in some lines.... but the earlier it is the shorter they are..... my advice is also do Harry potter first in islands of adventure, that area gets very congested ad the day goes on....
they usually also have one park or the other open early for resort guests..... so check the hours.
imo get a park hopper for every day, there are days where one park is busy and the other is not randomly, it's easy to get between parks.... the hogwarts express which goes between the 2 is also a different experience in each direction, you can only ride with a park to park ticket.
in the studios of you like the minions do that first..... line grows fast and long.
there ate some cases where the lines are short so don't waste the express pass..... not sure if you're limited to one use of express pass per attraction...... my pass includes it after 4pm.... but once per ride.

food.......mythos is awesome, refillable popcorn buckets are the cats meow and uber cheap. get a refillable mug....8 bucks all day refills every 10 minutes..... powerade/ soda/tea etc at the coke freestyle machines....you can have get them with your meal plan if you get that or get it separate.
there are free lockers available for when you go on a ride but won't fit big bags generally....

we can usually do both parks by noon if we get there at opening.
you'll also want to check what nights the horror nights is going an at the studios..... those days the park closes early and you'll need a horror night ticket to attend....i HIGHLY recommend getting the express pass for horror nights of you plan on doing more than 2 houses.....