The Anchor on Bankside is one of London's great riverside pubs — a rambling 18th-century building on the south bank directly opposite the Tate Modern, with views of St Paul's Cathedral from its terrace. Samuel Johnson drank here. Samuel Pepys watched the Great Fire of London from this spot in 1666.
The pub is big enough that there is usually space, which is not true of most Thames-side establishments. Order a pint of whatever is on cask, find a spot on the terrace, and watch the river. The food is decent pub fare rather than anything special. The setting does the work.