7 Days in SEA - What to do?

My friend and I (F, early 20s) will be traveling together to Vietnam and/or Thailand together for a week (12/26-1/1) and have no idea what to do! It'll be my first time traveling abroad in a while and we're very much into beautiful sights, fun activities, and delicious food! We specifically love picturesque spots, active things, and being adventurous with fruits and (safe) street food.

Does anyone have any fun stories, recommendations, or thoughts? We are mostly debating if we should go to just one country or split our time in both (depending on what would be cheaper and more fun). Thanks!