Bonser attended Gibbs High School in St. Petersburg, Florida. In four years he compiled a record of 24-9 and a 1.99 ERA. In his senior year, he went 7-3, 1.88 and hit .523 with 11 home runs. He was named the 2000 Pinellas County (FL) High School Player of the Year and played in the 2000 Florida State All-Star game.