For me, it would be really nice for your service to work out something like "You make 60g of coffee on Saturdays and Sundays, and then 30g's on Wednesday" and then work out when I'll be running out, and maybe order me a new bag to come in on Friday because it knows I'll likely run out on Saturday.
This doesn't seem super hard to do, but does seem like something that's important to work out, since there's a lot of products that people don't use on with regular daily amount.