Yes you can take food in.
The first bit is timed.
- A pre talk
- Then entry into the Great hall
- Then ushered on to the first half
First half you can do at your own pace but once left you can't go back in.
- loads of sets and set designs
- green screen area to ride broomsticks & flying car (photos cost ££)
- a place to practice your own spells
Then through to café area. Butterbeer on sale (1 is enough for all of you, it is an acquired taste I think). Can buy food (not a great selection) or eat your own.
Outside café area are large items - Dursley's house, Knight Bus, etc
You can go in and out of outside area and café.
After outside area is second section. Again once entered you can't go back. Lots of stuff on make up, costumes, animatronics. Model of Hogwarts.
Exit then shop. (£££)
If you arrive early you can go into the shop first if you want. There is also a café before you enter if you want, don't know if you can eat your own food in that bit.
We were there around 4-5 hours. My DDs aren't known for looking at things in great detail, and some wasn't suitable for youngest who had only read the first 2 books at that point (and only seen those films).
Even DH who is not a HP fan enjoyed himself.
Have fun.