that gar's back isn't kinked is it? looks like there could be some damage but that could just be the angle of the shot. the tankmates are also not a great choice for gars...pike and sunfishes generally don't get along well with each other (they will for a bit until massive size differences cause aggression issues) and are too skittish or aggressive to be kept with gars long term.
that being said, some fake plants rooted to the bottom will work, and i have always used water sprite for floating plants. this will block too much light from spooking the gars by giving overhead 'security' to them. bottom driftwood isn't necessary since it will just serve as an obstacle the gar can run into...small pieces are ok though.
don't get your driftwood from a lake or pond or river...buy a piece or get some from another aquarist. the wood one buys at the store is made to go into tanks, the wood in native aquatic ecosystems is in a state of decay and will eventually seriously throw off your whole tank (sometimes much sooner than later).--
--solomon