stay with in site of shore, storms with 8'-10' seas can come up with in minutes, especially if the winds are coming from W-NW-N across the lake.
as for GPS, i have the Garmin Etrex Legend. Water resistant, small and works great. Also had the Etrex Vista for my last job. I never needed the extra memory but see that it could come in handy if you wanted to download maps.