I would recommend against skipping lunch. Instead, adjust what you bring for your meal based on weather. I just worked all day yesterday in the sun and heat. For lunch, I brought light, easily digested food that would replenish without making me feel sick.

Blueberries and strawberries are great because they have nutrients and moisture. Fruits and veg tend to digest well, even in the heat. Hard-boiled eggs sit well with me and provide some nice protein. I also like the flavored tuna pouches with a few crackers.

I avoid food with a lot of fat/grease or dairy. Neither digests for me well and dairy even makes me feel sick in the heat.