Avoiding the slot machines and fair ground rides why not try
Felixstowe Viewing Area and watch the biggest container ships discharging their colourful boxes at the Viewing Point and take a walk on Landguard Common. The parking here is for free.
In the afternoon take the other end of FXT and park on the Cliffland Car Park (Parking fees apply) and take a walk to the Ferry and back. If you want to entertain the kiddies here there is crabbing from the jetty and a beach.
I'm now off there bucket and Spade in hand, young at heart [68]