The start and finish of the 10k will be along the Central Avenue of the park - if you head for the Bandstand in the centre you should be able to see the club tents and flags set up.
The tenderfoot will also take place on Central Avnue, and the fun run/relays on the playing field just behind the club tents.
The closest free public toilets are a short walk from the Bandstand in the centre of the park, and there are others located around the edge of the park. Changing facilities are available at the Millennium Arena track, but there is a charge to use them.
By bus: 19, 30, 44, 49, 137, 170, 239, 319, 344, 345
Rail: Battersea Park (15 mins walk) or Queenstown Road (18 mins)
Tube: Sloane Square (28 mins)
Information about parking is available here: http://www.wandsworth.gov.uk/batterseapark