When you tell someone you avoid certain foods due to an allergy or an intolerance, about half the time, they respond with, "What do you eat?" The smartass in me wants to respond with "Food."
People find it hard to believe that we can eat a lot of the same foods and be gluten/dairy/corn free. The catch is, I have to make a LOT from scratch. I don't buy cake mix or muffin mix. I make hamburger buns, salad dressing, dairy free yogurt, etc. I had to make Felix's dairy free margarine, because even the dairy free ones on the market contain corn. But, most of it is easy.
There are thousands of recipes for salad dressing on the internet. I even found one for dairy free ranch dressing that uses homemade mayo (you can buy regular mayo if you aren't avoiding corn or eggs but can't have dairy) and Felix loves it for dipping veggies. It maybe takes me about 15 minutes to whip up, and most of that time is waiting for my food processor to whip up the mayo. If you avoid several foods, click on that link and surf around, her blog is amazing, and she even posts meal plans so you can get ideas.
There are tons of things on the market these days that are gluten and dairy free. Most of them, we can't use because of the corn issue, but don't let that stop you! One thing to remember, though, is that all whole foods (fruit, veggies, meat) are gluten free, as long as they are fresh and not prepackaged. (The jury is still out on baby carrots) Many companies are jumping on the option to label their products gluten free, especially the ones that have always been gluten free. Many types of chips, sauces, or even hot dogs now are labeled gluten free. And, if its not, be wary. The reason is, it may not actually contain gluten, but if it is manufactured in a plant where they also make something containing wheat or other glutenous grains, there could be trace amounts of gluten in them. Some people can eat these foods and be completely fine, but some, like Felix, eat it and react just as badly as if they had eaten something made from wheat. If you are starting out on this gluten free journey, avoiding them is your best bet. That way, once you see how good you feel without it, you can try it and see the difference.
Everyone has different tastes, but after trying many different products, we've gotten pretty set on brands for certain foods that are gluten free. Its no longer a challenge for me to go to the store, and I don't spend hours reading labels while I'm there. If you are just starting, know that there is a light at the end of the tunnel. It gets better and once you get your bearings, you can handle just about anything.