Spend stamina pots in any events that gives you good rewards..
Monthly event, character plate event, ramen event, fishing event, treasure key event..
Just decide first if the rewards are worth spending, then use pots if needed. Stamina pots should always be saved for events such as those above.
The small exp boost that you get in monday will become pretty irrelevant as you level up higher. And recently, we got some permanent events that gives good amount of exp.
And yeah, dont forget to use your judgment about whether the rewards are worth spending pots for. Last plate event and this fishing event - I pretty much ignored them since there was nothing that I needed.