I second Mary Jane's chippie as the best!
Actually, for top crabbing go along the coast to Blakeney quay or Wells quay.
Good free outings include the pinewoods at Wells Next the Sea - park in the beach car park , not the quay, the bird obeservation / ecological exhibition places on the coast road at Cley, and at Morston, .
You can get a ferry to see the seals from Morston quay (book tickets at the pub in Morston, or on Blakeney quay - check times in advance by googling Bishops seal trips or Temples Seal trips, because they only go on high tide. Not ever so cheap - but worth it unless it is very windy or rainy. Wrap up warmer than you think!
Other good places are the Shire Horse centre near Sheringham, The Gressenhall Museum of rural life - mock up poorhouse and sweet shops as well as lots of farming stuff, and if it is very wet, the Steam Engine Museum at Thursford. The steam engines are all indoors, and they have a selection of huge old steam driven dance hall organs which they play in turn, steam roundabouts (indoors) and traction engines. There is an indoor soft play area at Wells. For bright autumn days the beach at cromer is fine, especially when the tide is out, or head off to Wells beach for wide open spaces, pine woods, dunes and wonderful beach huts. For pub lunches try the Kings Head (I think that's what it's called) at letheringsett, which is reputed to have a big childrens play area and climbing frame, or the king's Arms at Blakeney with a garden with swings out the back..or any of the coastal pubs, really.
Cromer and Sheringham are small traditional seaside towns - very charming and neither highly commercialised and arcade-ised, nor the 'Hampstead on Sea' of Burnham Market and the more villagey places. North Norfolk is a great mix, actually, having cottages and caravan sites and second homes in equal quanitites!