What did he like to do? Did he have a favorite place or a favorite thing to eat?
I like to celebrate people by doing or seeing their favorite things...things that they would be happy and proud of me doing. So, for example, when my aunt and grandfather-in-law both died of cancer within a year, we signed up for Relay for Life, and while there, we split a peanutbutter and chocolate ice cream bar (his favorite flavor...yes, calories were high, but I walked a full marathon in those 24 hours, so I'm OK with it) and listened to music my aunt would enjoy on my headphones while I walked.
Can you go somewhere he liked to go? Can you cook something he liked to eat? Think back on things you did together, things he liked to do, and etc, and come up with a plan that honors those things he liked. And then schedule some time to take care of yourself, too...you know that he would want you to, right?
Lots of

for you.