It is so satisfying coming home to a clean kitchen without dirty dishes. If your roommate is having a busy morning and you don't have many plans in store, take his/hers dishes to help. Your roommate will definitely appreciate this and thank you!
Clean your roommate's room
If you anyways are cleaning your own room, you might as well also just go for a quick round with the vacuum cleaner in your roommate's room. It won't take more than a few minutes and it will be a great help for your roommate if s/he is having a busy period and not much time to clean self.
Clean the kitchen cupboards
If you have spilt up the cupboards in the kitchen between you, and you are cleaning your end of the kitchen, just take a wet cloth and go over your roommate's cupboards as well.
If you are about to do some laundry yourself ask your roommate if s/he want's something washed as well now that you anyways are going to wash.
If you are home one day and your roommate is not returning before dinner, make dinner for you and your roommate to enjoy together when s/he comes home. It is so great to come home and not have to think about making dinner first, so there are many points to score on the roommate account here!
Get pizza when your roommate is hung over
Pizzas and hangovers go together! When hung over you just want a pizza, but mostly you are too tired are careless to wanting to put on shoes and go down to the pizzaria to get your pizza. So save your roommate the delivery fee and go down to get the pizza for her/him.
Go to the bakery Sunday morning
Who doesn't love a freshly made bun with butter and cheese in the weekends. Surprise your roommate with nice bread from the bakery and perhaps a croissant or two for the coffee.
Bake a cake
It is always nice to have cake in the home. Surprise your roommate with cake after work or school! Enjoy it together while you talk about your day.
Help when guests are coming over
If your roommate is having guest over for dinner, offer your help! You can either help setting up the table or even help with the dinner.