If you remembered to pack a needle, but forgot a spool of thread, and a field repair is in order: go see whether you packed any dental floss. If so, you have some hardy thread indeed, and if you bought the green minty kind, you may discover a whiff of mint now and again emanating from your repair site. I try to remember to buy the old string type of floss rather than the newer kind with flat bits, but if your needle has a big enough eye, you can thread either sort. Careful now, too thick a needle may give you threading holes larger than you want. If the repair is in a location that may leak, there are a wide variety of different things you can use to seal your sewn repair and enjoy a drier tent interior. As my preference is for canvas tents over nylon, I use beeswax, but I think a silicone spray would nicely seal a repair to nylon.

I've found that small bungee cords (or the poor-boy version, an old bicycle inner tube cut with a scissors into very many tough rubber bands just as thick or thin as you wish) is a great add-on to tent and tarp guy lines. When those big gusts of wind arrive, the elasticity of the added-on stretchy thing allows the wind to buffet the tent or tarp about, but prevents tent stakes from being dislodged, or tarps from becoming shredded. No stitches are needed when the elastic, instead of the fabric, takes the strain.

Without being certain, I suspect that exposure to prolonged sunlight weakens the plastic in these chairs. It sure seems to cause fading of the color, and while I've slain some faded ones with my bulk, I don't recall having broken one that hadn't already been more than one season exposed to the elements. Perhaps a canvas or vinyl cover over a stack of these, if they must be stored outside, might tend to prolong their useful life. I'm not aware of any adhesive that would join such broken bits securely enough to risk another sit in a repaired plastic chair.