Sometimes it feels like the simplest thing would be to stay home and get all your food delivered and never spend time in the contaminated wheat-ridden world. Getting people to shower and change when they came to visit would be nice. However, if this doesn't suit you, there are some precautions you can take to making it a little more likely you can enjoy your friends company and not spend all your time gazing at the door of their loo.
Take some food with you. People get uneasy when they are eating and you don't. Pack something that you can eat while holding the wrapper so that you reduce the chance of getting gluten on your food from your fingers. Remember, their sofa, chair back, novels, baby photos...all will be covered with invisible gluten. Their cutlery will live in a drawer that has crumbs in it.
Don't allow your niceness to persuade you to eat food made specially for you using normal dishes.
Accept a tea or coffee unless you have an important day following, but be aware that unless they use a dishwasher you will probably get some gluten contamination from the cup.
Take some glutenzyme capsules with you. Before I discovered these I couldn't spend an afternoon with my friends as the gut ache would start after an hour, and the brain fog an hour later, even if I didn't eat or drink anything. Taking one of these every hour allows me to enjoy my afternoon. I buy these off the Internet. Make sure you get ones that are lactose free if necessary. You can order them from your local chemist. With these I can stay for several days at my sister's house, without them I need to leave after a couple of hours (and she lives a five hour drive away; being able to stay is good).
Chose the right clothes. Wear elasticated waistbands or clothes with belts where you can accommodate a sudden six inch increase in waist size. Wear a long loose top so that the resulting gape between the zipper halves will be hidden. A long loose dress allows a lot of expansion.
Carry hand wipes with you. You can clean surfaces and hands. I like Sani-hands, which have a textured surface on one side which is great for scrubbing. I buy them in bulk off the Internet and always carry some.
Encourage people to eat as a separate activity from handling things. I meet a group of friends who share an interest in the wilder end of embroidery - we look at each others work with clean hands and that reduces the spread of gluten. I have handed someone a wipe and got them to clean their hands before looking at a book of mine...people do treat bread and biscuits as if they were clean items when the are not.
If you do get minor contamination, fennel tea can help with the colic, as well as medicines from your pharmacist. If you have a day when you need to leave the house and feel well enough to go out, an anti-diarrhoea medicine can help give you some time.
Of course, a full scale contamination probably means you wont be able to do anything else for days, but the minuscule invisible contamination issues may be manageable with some of these tips.