I don't sew. Is there an easy way to cover outdoor sofa cushions?

Try fabric glue

Yes you can iron on seaming tape that will work well available at craft and fabric stores

You can close the seams with double sided sticky tape (depending on the type of fabric), there is also a liquid seam product (works like glue, hold the fabric together with clothes pins until it dries) or there is another type of seam sealer that can be applied with a hot iron. It comes in sheets or on a roll. Place it between the fabric, wrong side together and press it really well with a hot iron, the turn it right side out, place your cushion inside. Fold the open ends of the fabric to make a neat edge, place the seam sealer between those edges and press them with the hot iron.

I used the tape on some and they actually lasted years. Was surprised

The tape is really great...

Thanks for these great suggestions!

Sheets and the clips to hold sheets onto bed that go underneath.

easy isn't always right. they can be wrapped then taped with duc tape. it won't last long because of the heat of the sun, and it won't look the greatest, but it functions.

If the cushions are going to be used outdoors in the direct sun, or high heat, don't use any glue or iron on tape, as it will melt, get gucky through the fibres, and leak out. Choose a fabric that is light coloured as it will fade quickly.

If the cushions are going to be used outdoors in any climate where it is humid, or you do get rain, then don't use any fabric that is not designed for outdoor use, as it will acquire black mildew, won't dry out properly, likely rust stain, and eventually disintegrate.

While it is not necessary to pay big bucks for high end brand name fabrics, such as Sunbrella, good durability can be had by purchasing either vynal backed curtain fabric, or water resistent fabric shower curtains.