I've still got one of the original plastic "hand planes" from back when they were called "hand guns". I got it for free from a company trying to drum up interest. Pretty fun. I think a lunch tray would be hard to grip.
never used one in the water, but if you have a a front wheel drive car get two from mcdonalds or somewhere and drive the back tires onto them, pull the parking brake and ensue fun parking like spinning and donuts
handplanes cost all of nothing to make yourself... I used a skateboard deck I broke in half and shaped it down to a plane with concave that lifts you out of water when you get going. used a old leash tat broke as the handle.. screwed it to the board with shallow screws. Only broke it out a few times but do remmeber having a blast with it one day with pounding clean shorebreak.
I remember back in the day seeing Eric Anderson (former boogie God of the late 80s early 90s) at the 14 St Pier in VB doing like 360's and sht on a Micky D's tray he got at the restaurant right there. If you don't weight much it's easy and fun.