I have some big stickers that I put on my child and can also go on his lunchbox. I have some from Mabel Labels. LabelDaddy has them too.
Plus I ordered some custom ones that were a white background that had the medical alert symbol plus the allergies. Unfortunately, I can't remember where I got them. They worked well for dark shirts, since a lot of the allergy stickers are red instead of white. I had to order custom ones because he has multiple food allergies so the stock peanut ones weren't enough.
You could probably make your own if you wanted to and had a computer with printer. The custom white ones that I got were just round stickers and a cut-n-pasted image of the medical alert symbol with some text.
Santa also brought a medical id bracelet for my son (and an identity bracelet for his brother that is not allergic). But, so far we are having a hard time getting him to wear it. We had it re-sized (links removed) because even the small size is big. My goal is to get him used to it this summer because it will be a drop off pre-school next year and not parent participation. I like the bracelet in case something bad happens it has my phone number. I do agree with others that people won't notice it easily so a big sticker (maybe even front and back) is probably the most visible.
I think my son would like to wear a neck (dog tags) one but I worry about the strangulation issues at his age.
Allermates has cards for giving out at restaurants. You could give those to his teacher and friends. It's two sided so take a look at both sides of the image to see if you like them. I'm planning on laminating some. Here is the link: http://www.allermates.com/restaurant-cards.php
As far as educating, we have been teaching him to ask if something has nuts in it and if he isn't sure, not to eat it. He is good about asking, but he would also take something if someone just blindly said it was safe. I also bring extra snacks for school so if the school snack isn't suitable, he has something to eat. At the parent participation school some of the parents are bad about it and I've had to nix stuff....especially the stuff they just bring in from their cupboard in a ziploc bag. For birthday parties and such, I make and bring a safe cupcake for him. If there are multiple birthdays coming up, I freeze some so I don't have to make a full batch again.
You could try making a sheet for his friends house that explains what is and isn't a safe food as well as safe practices and what to do if there is an issue (benadryl / epi-pen).
For example, where to look on the ingredients to see if it contains peanut, may contain peanuts, may contain trace peanuts, processed on a machine that processes peanuts, and/or processed in a facility that processes peanuts. Also, point out that if it doesn't have anything in bold at the bottom about allergies, they need to look at all the parenthesis ingredients listed. I've only seen that happen once so far. Also, I've seen a brownie package list on the front that it is free from a bunch of allergens and then the ingredients list said it was made in a facility that processes the allergens.
For safe practices, you could explain about cross contamination and ask that peanut butter not be served when he is there (even if he isn't the one eating it). Or the restaurant cards may be suitable for this.
If he has an epi-pen, make sure the adults where he will be know how to use it. They all come with trainer pens so you can show them how before leaving him. I had some expired full ones so we tried them out on an orange. It was actually a useful learning experience. The real epi-pens make a loud click when the injection goes and there is a tendency to pull back instead of leaving it in for 10 seconds. It might be worth emphasizing not to pull back. I also always bring 2 pens.
Initially, I typically offer to bring a snack for him when going to a friends house. Overtime, his friends parents have gotten good about asking what he can have. My family actually takes pictures of the ingredients lists for any baked products, texts it to me, and asks me if it's okay. :-)