DS is 8yo. He brings his own lunch to school and he has a safe snack in case of birthday parties at school. In his class there's one kid with a tree nut allergy, one kid with a peanut allergy, one kid with a strawberry allergy, and him (no gluten, dairy, eggs, soy, chicken, apple, orange, tuna, almonds, and lots more).
Last night the father of one of the kids in his class called and asked if Simon could come over this weekend. I said sure and asked when. He said 11 o'clock and they could feed him lunch. I said, "it's easier if I feed him lunch first and then bring him over." And he said that his son told him that Simon had a lot of allergies and that he liked meatballs (since most sauce has citric acid in it and who knows what else they put in their meatballs, it's still not happening). I said I'd send him with snacks. His best friend's mother makes food for him. And she has all the safe lists from me. She's vacationed with us and knows the drill. For birthday parties here, I try to do something that is versatile (like tacos, where you can do wheat or corn tortillas, some people can do cheese and sour cream, etc.). A few weeks ago he went to a birthday party at a laser tag place. I sent along lunch and a cupcake (they were having pizza). When basketball season ended, the coach gave each kid a goodie bag (his had a nerf ball, stickers, and $2 and the coach said that was because he couldn't have the candy he was giving to the other kids! Simon thought that was GREAT!) and then took them out for pizza at a local place (again, he brought his own lunch). It doesn't keep him from being social or from being invited places. He's very good about it and knows what he can and cannot eat.
DD2 is only 4 so she's not being invited to birthday parties yet (thankfully). But when we go to family ones, I'll bring cupcakes for them both, or So Delicious coconut milk ice cream for her, or whatever. And our food. My family is pretty good. We do family dinners once a month, and it's always safe for us (my brother and SIL are very good about it, previewing recipes with me). At nursery school, they rotate snack among the parents. I see what's on the list for that day, and say whether she can have it or not on the sign-in sheet, and on days that it's my turn, she gets to share her kind of food with everyone.
When we go anywhere like a mall or amusement park, DD2 wears a Velcro ID bracelet that has my name and cell phone on it, and in huge letters it says "DO NOT FEED ME -- ALLERGIES" (that should scare the kidnappers away since I don't say what food).
Sometimes my 8yo will say "it's not fair" about how he can't have the ice cream at the ice cream social that day. And I say, "I know it's hard, but I can't either." And then I'll say, "it's not fair that daddy can never have a cat" (they cause asthma). "It's not fair that (your friends) Noah and Riley have diabetes." "It's not fair that Uncle LG only has one leg." Everybody has something unfair, that's just the way the world is. And he gets it. DD2 has only known a life with a restricted diet. She doesn't know anything else. So for her it actually seems easier.