When Jim and John are in the restaurant, John tells Doris and Molly that Jim was trying to enjoy his "grass widowerhood". A grass widower (or widow) is a man (or woman) whose spouse is away.
Slot machines were first invented in 1894 by Charles Fey. By the time of this film, they were commonplace throughout England. The design shown here is what the original machines looked like, and jackpots were modest, unlike the digitized big payout models of today.
The couple indulges in the most British of summer traditions, a picnic luncheon by punt (a traditional river boat, propelled by using a long pole in the water).