Freeze Water Jugs or Bottles and add them to your Cooler instead of Ice Packs. Once they melt, you will have drinking water! Tons of awesome Camping Ideas!
For the outdoor bench cushions How to Make an Easy, No-Sew Cushion: Not washable, but much faster and cheaper (less fabric)
"How to Create Waterproof Seams. Protect a vinyl tarp cover or give anti-wick thread a try!" May work on diy dog beds made with waterproof canvas.
Knots can be very useful. They can be used for boating, construction, and various DIY projects. This video covers seven essential knots.