I can't believe I haven't posted this activity before, but I can't find it anywhere. I use it frequently with many variations. You will need some spots.
Throw down the spots outside the court sidelines about five feet apart starting at net position and progressing until the last spot is behind the baseline in the usual serving position. Players take turn serving from positions within the court aligned with the spots, starting with the 'head' of the caterpillar (the position closest to the net). Players move back one position for each serve hit in. A missed serve means player goes all the way back to the first position closest to the net. First player to reach baseline and hit a serve in, wins.
This game is easily converted to a team activity, with players on each team taking turns hitting. In other words, no fair having the same person on the team hitting all the serves! Whether playing individual or team, play best two out of three and switch sides (deuce/ad) each round.
Hint: when you are laying down the spots, try not to put two of the same colors together. It gets confusing trying to remember who should be serving from which spot/color. Having each position a different colored spot helps everyone keep track.