Felixstowe is one of the few ports with an official viewing area. It is at Landguard Point, accessed, funnily enough, along Viewpoint Road. There is parking, and a snack bar, but no toilets. Everything moving in and out of Felixstowe, Harwich, Ipswich and Mistley passes right in front of you, the only problem for photography is the sun, which can be a problem in the afternoons. Oh and the seagulls, which also like to have their photographs taken!!!
If you haven't a car, there is an hourly bus service which originates in Ipswich, but passes through the town by the Railway Station, and, in season, a foot ferry from Harwich.