I used to stash oil, until I realized that I end up with weights I really don't want to use. I also don't like to mix brands together for a fresh oil change, and I like to buy and oil I want to try rather than use whatever I have.
The only time I will buy it is if it is super cheap and in a grade I will use. 5w20 or 5w30, some 10w30 if it is the good stuff. I still have a batch of the old super low noack ultra in 10w30. I never buy any 10w40 or 20w50 stuff, that's just silly for me as I have 0 applications I want to use that in and I have no desire to blend it with thinner oil.