A pair of old skis are still useful if they still have a flat running surface, a sharpish edge and are rigid enough to form the base for a multi-person toboggan. Here's how one builds such a toboggan.
The objective of this toboggan design is to:
Be as light as possible
Be as strong as possible
Be as fast as possible
Send 2 adults or 12 very small screaming children down a hellishly steep hill
A pair of knackered adult's skis
A 8'x4' sheet of 9mm birch plywood
Strong contact glue
The usual workshop bits and bobs and consumables
Circular saw and cutting guide, or table saw
Router with spiral cutter
Clamps (you can never have too many!)
Step 1: Strip an old pair of straight-edged skis
Remove the bindings with a large star-point screwdriver and throw them away.
Use a belt sander to roughen the top resin layer to create a glue surface. I went deep enough to remove the faded branding under the resin. This exposes a light plastic material that may in your case be slightly porous, so it you sand this deep, be sure to thoroughly cover the exposed surfaces with polyurethane varnish in the last step.