Q. If you travel Chol-Hamoed and take with you a pop-up suka, that has a floor area of about one square meter, can two or more people stand there or sit on stools at the same time and eat?

A. Horav Shlomo Miller’s Shlit’a opinion is that once a suka has the proper minimum size of seven by seven tefachim (70cm. By 70cm.) it is kosher and as many people that are able to seat inside with some comfort are permitted to do so. He mentioned that you need a small space for a minimal small seat, box or similar (about 10 sq. cm.,) that can serve as a table.
See also question 373 on this forum quoted bellow
A. Shaarei Tzion (634: 7) permits one to eat in the Suka from hand to mouth without the benefit of a table. However he seems to contradict his ruling in Mishna Berura (640: 27) that one should leave the table in the Suka when sleeping (Suka Kehichoso 9: 6 and Shone Halochos 640: 5, see also Moadim Uzmanim 1: 87 that disagrees that one must leave the table in the Suka when sleeping at night).

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a.