this is the obvious one, but easily available silk will allow a wide range of uses for cloth, the expense of silk is what normally limits its uses. Clothing, Bags, upholstery, rugs, bedding, curtains, are all possible. But cloth offers other uses besides clothing. Silk sails would be stronger and lighter. Tents made of silk would be much lighter and more water resistant. The best parachutes are made of silk, as are the best bags. Silk windmill vanes would work better and medieval cranes using silk would be safer. Artillery powder bags used to be made of silk becasue the was the only cloth that would burn completely and not foul the guns. Depending on how loose you want to play with technology silk and rubber tires are also possible, silk and rubber bicycle tires are some of the best available.
Rope and string are used everywhere in medieval society, making rope that is stronger and easier to make will be a big impact, one of the major limitations of rope was how long it took to make, your spider can literally spin rope on demand. Even things like fishing nets would be improved. One big advantage is sutures, silk sutures are stronger yes but the body can also break down so you have self dissolving sutures a few hundred years early. Rope bridges (suspension and hanging) become easy to make, block and tackle become cheap, building becomes easier, there are many small impacts this will have.
Armor was made from cloth and paper, such armor was cheap and offered real protection, cloth armor will stop a sword, but tended to be bulky. Silk could be uses in the same way and it would be much stronger and thus much lighter and less bulky. Silk gambeson may well become the norm. It also would not need leather for fittings, silk is tough enough on its own.
Silk paper is a real thing, it has advantages and disadvantages. it is less easy to write on and harder to make, but is tougher, it is also much fancier so it is often used for expensive goods. But it could be uses again for armor, it is stronger than normal paper allowing for lighter less bulky paper armor.