I sympathize with picky eaters, because I was one... and to some extent, I still am. Here are some suggestions for packing lunches for picky eaters. Note that these are from the Toddlebug years of Basic Bento and are not necessarily gluten-free.
-- Start with what you know will be appealing, and go from there. That means not just particular foods, but ways of cooking (Toddlebug will try ANYTHING in a stir fry) and presenting (who can resist little bitty shape cut-outs?).
-- The hungrier the kid, the more of a stretch you can try. That makes lunchtime after a morning without a snack a great time to include one item that your child might not eat at home readily.
-- Set aside a portion for your child before adding sauces, herbs and spices.
-- Serve items separately instead of together. Many children who won't eat a casserole, for example, will eat a few bites of noodles, a little chicken, a little cheese, and a little of the vegetable if they're served separately.
-- Put a vegetable in the lunchbox ten times (not in a row! but within a few months) before you give up on that one. Do not give up on vegetables at lunch altogether.
-- The younger your child is, the more you can expect to see improvement if you provide good choices as often as possible.
-- If you haven't read Child of Mine by Ellyn Satter, I recommend it highly.
Ideas to get you started:
1. Pasta salad (maybe just pasta, homemade Italian dressing, cucumber and tomato; cut-up cooked chicken or tuna if s/he'll allow it!). Try WackyMac or something so you have different colors.
2. Banana rolled up in a wheat tortilla with peanut butter, sliced to look like sushi
3. Veggie burger strips (or shapes) with a sauce she likes for dipping (mustard? BBQ sauce?); wheat bread cut into shapes with a cookie cutter.
4. Homemade chicken nuggets/fingers (Google for a healthy recipe)
5. Mini quiche or fritatta
7. Pancakes or a waffle, with sauce/syrup in the dip container and strawberries or blueberries on top
8. Pizza, if s/he'll eat it at room temperature, or stromboli
9. Tortellini or ravioli, either with red sauce or just butter or olive oil
10. Turkey mini meatballs with sauce for dipping, such as honey mustard.
11. Deli turkey (I like Hormel Naturals) rolled up and skewered on toothpicks, with cheese if desired--Here's somebody who did that as a breakfast side, but with bologna.
12. Homemade Lunchable (crackers, cheese, meat?) with applesauce and a veg on the side (edamame?)
13. Do a PB & J with a different kind of bread, a different kind of jelly (we love blackberry preserves), or a different kind of butter (like almond butter)
14. Leftovers from dinner a night or two before.
Interesting sides to try:
* Cornbread or polenta
* Whole wheat English muffins by Nature's Own. They look like health food, but they taste really good.
* Different kinds of muffins: pumpkin, zucchini, etc. You can also do mini muffins and include two or three.
* Cantaloupe or other melon
* Blueberries or other berries; grapes
* An orange or clementine--peel and section and de-seed it and s/he's more likely to eat it.
* A ripe plum, pear, apple (I like Fuji), or peach. Slice for young kids or those with braces.
* Edamame (out of the pod). Looks like a lima bean, but NO! These taste great! And you can buy them frozen and just use the amount you want.
* Canned pineapple or peaches or whatever she likes, drained. Watch the label for added sweeteners and color, especially on fruit cocktail.
* Cottage cheese--if s/he doesn't like it plain, try it with either pineapple or peaches or Italian seasoning, or try another brand. Some taste terribly salty.
* String cheese or cheese chunks. Try alternating with fruit on kebabs.
* Cherry or grape tomatoes. Serve on a toothpick to make them more interesting.
* Sliced cucumber, or any other veg s/he likes raw (cauliflower?) or steamed (green beans? peas and carrots?). Hint for cucumber: slice as much as you can stand up in the container, and then cut out a heart or two to put on top like this.
* Celery with cream cheese, PB, ranch dip (check ingredients), or whatever
* Mixed unsalted nuts, or almonds alone
* Granola bar/cereal bar--Check the ingredients if not homemade, though; some are junk food. Here's a recipe I'm going to try when I get around to it.
* Will s/he eat a hard-boiled egg? How about if it's shaped like a car or a bunny? Try an egg mold. They're inexpensive.
* Orange or yellow bell pepper cut into interesting shapes with your smallest cookie cutters. (If s/he's like me, don't bother with green peppers at all.)
* Minute Rice Ready Rice (brown) if it will get eaten at room temperature or can be microwaved--or make some sushi rice and mold it into a little circle with a 1/8 c. measuring cup. (See the Recipes and Tips page.)
* Tortilla chips and salsa or guacamole
* Raisins/dried fruit. Not so good for the teeth, so don't use all the time.
Have fun! Feel free to add more suggestions in the comments. What has worked for YOUR picky eater?