Boot toss. One person turns their back, the other person tosses a boot into a grassy field. Time how long it takes the first person to find the boot. Works best at dusk. Entertains our girls for hours :)
For us, various card games have been the most common. The card game SET used to be the most popular though poker using snacks as chips is fairly popular, especially with those who regularly win :). Go (using a cloth rather than wooden board) can be quite lightweight and compact. There are a various of board games which are designed for travel which are small and light, typically a plastic folding board with plastic pieces: scrabble, chess/checkers, othello, etc all run 3-4oz. In the past we have also brought tangoes, pass the pigs, and various strategic micro metagames board games from the 1970s.