Yes, the Kids with Food Allergies web site is a HUGE resource. There are many parents who manage multiple food allergies and have great advice. I find the regular posters there to be very knowledgeable with lots of btdt good advice. I strongly urge you to visit and read.
Is that your pediatrician or an allergist who advised you on the new results? Has your Ds ever reacted to nuts, shrimp or wheat before? A blood test alone should not have you eliminating food that he has eaten before without reacting. Reactions always trump test results, so has he eaten wheat before? I am guessing that he has at his age. Of course you know your son/Dr. best but its something to consider. I wouldn't test out shrimp/peanuts if those are new but I wouldn't pull wheat without questioning my doctor more unless you really feel like he is reacting. I think you mentioned that he has reacted to eggs before. Does wheat do the same thing?
We have egg, dairy, and peanut allergies, and a whole lot of otherestrictions. We've done wheat free before and its not fun, but it wasn't awful. You can often replace with corn products (or rice, quinoa, oat).
I have not found a good cookbook for kids with multiple food allergies, because so many of them focus on eliminating just one group (nut-free or dairy free). The Web site suggested above does have a fee based (I think) recipe index where you can look up recipe ideas based on your specific allergy set. Its the best option I have found.
We have at least 3 sets of Epi-pens. 1 for preschool, 1 for the bookcase at home (it never moves from that spot), 1 for me to carry in my purse. I did not buy any special holder for them and haven't had a problem in the last 2+ years with them bumping around in purse/backpacks/lunch bags. You do need to protect Epi pens from extreme heat/cold so they shouldn't sit in cars, in front of a heater, etc.
Until you become familiar with safe options at restaurants, it will be important to carry safe snacks with you everywhere. In the early months I relied a lot on dry cereals and dried fruit because they didn't spoil and I could keep them in the my car/purse/bag, etc. Oat square, corn or rice chex, and fruit leathers, dried mango/cranberries/raisins. Since your Ds can have dairy, you can usually find cheese and yogurt as options.
Ds1 (2006). Ds2 (2010). Ds3 (2012).