Many hams will be working from home for Field Day, and most have FM capabilities. Even with an HT it may be possible of make a number of contacts.
Some suggested simplex frequencies: 146.49, 146.505, 146.52, 146.535, 146.55, 146.58, 146.595, 147.42, 147.435, 147.45, 147.465, 147.48, 147.495, 147.51, 147.525, 147.54, 147.555, 147.57, 147.585, 223.42, 223.44, 223.46, 223.48, 223.50, 223.52, 446.00