You can get a stool sample without going anywhere near your cat. From your email, it sounds as if he is an indoor-outdoor cat. I'd suggest you bring him indoors until at least after the vet visit. Keep him confined in a room with his food, water, and litter box. After he has pooped, simply use a Q-Tip or wooden stick (like a Popsicle stick) and scrape a small amount of matter from the stool. It doesn't have to be very large, a sample equivalent to a teaspoon or less is plenty. Put the sample along with the Q-Tip into a sealable plastic bag, and refrigerate it until your vet appointment.
Butt-scooting is fairly common, and worms, including tapeworms are sometimes the cause. Another potential cause is an anal gland impaction or infection, which can be serious, if left untreated. In any case, your veterinarian can test for both potential condition when he sees your cat. Since tapeworms and other parasites are carried by fleas, checking for fleas will also be part of the exam.
Hope this helps, and good luck to you and your cat. Oh, and to enjoy his company for many more years, please seriously consider making him an indoor-only cat.