I want him to eat well, have energy and not be hungry, but I also don’t want to fill him with unhealthy things. What should I put in his lunch box?
I’ve been doing some research and it seems like the best thing to do is to balance protein, carbs and healthy fats. For example, a whole wheat sandwich with cheese and turkey, a fruit like strawberries or grapes, and something crunchy like carrots or oatmeal cookies. I also thought about yogurt with granola, but I’m afraid it will make a mess in his backpack
Omg, I was exactly where you are a few months ago when my daughter started daycare. I obsessed over every little thing in her lunchbox, thinking it had to be perfect, nutritious, balanced, and something she’d actually eat. Spoiler alert: half of it came back untouched. 
Turns out, they eat differently at daycare than they do at home. The social aspect changes everything! Some days they devour everything, other days they pick at it. Give yourself grace, you’re doing amazing just by thinking about this!
the daycare lunch struggle is so real. It’s like this weird game of “Will they eat it today?” vs. “Will this come back untouched?” And then you feel guilty when they don’t eat enough, but also guilty when you send something too fun (aka unhealthy😅. It’s exhausting
I feel this! I packed this adorable bento box for my son’s first week of daycare, and by Friday, I was tossing in whatever I could grab. 
Have you asked the daycare what other kids typically bring? Sometimes kids are more likely to eat what they see their friends eating!
One trick that helped me was packing a safe food , new food combo. So something I know they’ll eat cheese, crackers, apple slices along with something I want them to try cucumber slices, hummus, etc… That way, there’s no pressure, and they always have something to eat.
Another tip: Test run the lunchbox at home! See what he eats when you give him the packed lunch one day before daycare. You’ll get an idea of what works and what comes back untouched. 
I went through this with my toddler, and after trial and error, I found a few go, to lunches that worked well:
Mini whole, wheat pancakes with almond butter easy to hold, not too messy
Cheese cubes, whole grain crackers, and some cut, up fruit
Veggie muffins I sneak in spinach and carrots
Hard, boiled eggs with some avocado slices
Also, if you’re worried about yogurt spilling, I started using freezer yogurt tubes, they thaw by lunchtime but don’t leak! Total game changer
Girl, I swear lunch packing is way more stressful than it should be. Why does it feel like a high, stakes event??
My biggest lesson learned, keep it simple. I spent so much time making Pinterest, worthy lunches just for my son to eat ONE thing and ignore the rest. Now, I focus on things he actually eats at home:
Diced chicken, cheese, and whole-wheat pita
Banana or clementine already peeled
Snap peas or bell peppers
A fun snack homemade banana bread or pretzels
Also, daycare teachers are magicians. My son wouldn’t touch a carrot at home but suddenly loves them because his best friend at daycare eats them. You’ll get into a rhythm, I promise