Do restaurants have to go boxes?

Hello!

I will be going to Japan for the first time in November. I plan to go to a lot of restaurants to enjoy the vast and wonderful food Japan has to offer. I tend to not eat a lot or finish the regular food serving in America. I understand that Japan has smaller food servings but if I am unable to finish my food do the restaurants/bars have a to go box/take out containers for their guest?

Thank you very much and sorry if this is a silly question.

Traditionally, not. Eat-ins are eat-ins, and takeouts are takeouts. Restaurants (where people sit down to eat from the start) usually do not provide "to go" boxes for taking the remainder home, for fear of people consuming the leftover far too later and the food going bad... But some do, so no harm asking :) And the food servings are smaller than in the US :)

By law, a restaurant needs a separate license to sell take-out food, and that includes providing doggy bags to eat-in customers. Most places don't have this license, but some do.

Sometimes smaller restaurants without a license will wrap up left-over food for you, but they are breaking the law.

Luckily very few restaurants serve the insanely big portion sizes that are common in the US.

In my experience as a local, most places will wrap your leftovers, upon request, apart from times when food poisoning such as o-158 become serious, which happens mostly during summer.

The custom can also be regional. For example, I have relatives in Fukui where it seems to be the norm to have leftovers wrapped, while here in Yokohama you sometimes get this request rejected.

Of course, there are certain things you can't take home because of the quality. For example, noodles usually can't be taken home, because they tend to get too soft in minutes.

Another thing is that if you bring your own box and discreetly put your leftovers in it on your own risk, the restaurant won't say anything about it. But it's wise and polite to follow the orders of the owners, especially when you don't know about the local climate.

Either way, when making your order you can ask, "nokottara take-out dekimasuka? (Can I take out if anything is left over?)"

Thank you very much everyone for your help!