You are too late.

As far as I rember yes they do.

yes there is

Hi Joanne H, There is an entry charge for the Castle Museum, detailed below: Adult (inc Seniors) £7.60 Child (Aged 4-16) £4.75 Reduced Entrance Fee - Disabled visitors and a carer; full-time students 17+; welfare benefit recipients; and serving Military personnel - proof of reduced entrance fee status required and may be requested on entry) £4.75 Saver ticket (great for families!) - For two adults and two children OR one adult and three children £20.00 There are also optional extras such as tours and digital tablet hire, which will enhance the visit. For more information about Castle entry and our Castle Pass, please visit the Colchester Museums website.

i realise this question is over a year old, but it seems that no one has answered and so, for future possible visitors, I can answer the question now! Yes, people can go in and out of the castle to get food from any of the nearby cafe's/pubs/restaurants etc - we just told them at the payment desk and they said it was fine - we already had our tickets for our tour, so only had to show those, if asked. However, always check at the desk to make sure, in case they change the rules at some stage!! The castle park is right next to the castle, and there are seats as well as lots of grass, where you could sit and picnic on a nice day :)