Almost everything about beach cricket is improvised: the playing ground, the rules, the teams (quite often there are no teams), and the equipment. A bat of some kind (not necessarily a cricket bat) and a ball (usually a tennis ball) are the only essentials. The pitch can be any stretch of ground that is reasonably flat, the wickets any convenient object of about the right size - a cardboard box, a rubbish bin, or (especially on the beach) an insulated drink cooler.
Beach cricket rules change constantly. Often they are made up on the spot. As always with informal games, it is the unspoken rules that are most important: these are usually that all participants should have a reasonable chance to play a part regardless of age, gender, or skill level, and that no-one should be injured. Typical examples of the less important but explicit rules for a particular game might include:
Beach cricket (and other similar games around the world) is one of the very few truly child-like activities that modern adults may participate in without attracting social stigma, and one of the dwindling number of adult activities that are accessible to children. The sociology of play, especially adult play, is a curiously neglected field, but a starting point is Roger Caillois' Man, Play and Games (University of Illinois Press, 2001, ISBN 025207033X.)