I'd give it 24 hours before discarding

Anonymous wrote:When we were kids everyone brought their lunches in brown paper bags. No ice packs. Many ham sandwiches.

ha.. that's so true.

I do this every day for 3 kids and have never thought twice about it.

Anonymous wrote:I think it’ll be ok! I’m sure others will chime in that you’re being a helicopter parent and have anxiety but I think about things like this too, and I see no harm in asking others about food safety.

+1

Mayo does not need to be refrigerated....at all, ever, even if opened.
You should be more worried about the ham. If it is salami and cured and smoked also can last almost forever.

Anonymous wrote:Mayo is oil, egg (denatured) and acid. Its going to be fine.

I would be more concerned with the deli meat, frankly.

Yes! As long as the it's commercial (not homemade) mayo, it's fine.

Depending on your source of preference:

https://dressings-sauces.org/food-safety-facts/

https://www.thespruceeats.com/mayonnaise-spoilage-myths-and-safety-1808083

https://www.epicurious.com/ingredients/the-truth-about-mayonnaise-and-food-safety-article

I took a mayo/deli meat sandwich to school almost every day in the 80s/90s and used a brown paper lunch bag daily. I never got sick.

I'd say over night is not a good idea or leaving in a hot car is not a good idea. Room temperature is fine for awhile.

I did this once and was worried about food poisoning, but my kid was fine.