basically, what buttlover said, store until you have 50 to use for a stamp card for next month. also I'd suggest expanding box slots (make sure you have 30+ free slots if possible) and spending the rest on charisma/stamina refills (and maybe exp buff, so you level faster = reach big hero title earlier as well as get more max stamina to use with SC-stamina refill during events next time), which includes farming DC for spica btw.
aside from the first 10 summons, you generally won't need to summon again for quite some time. getting event units and gold/silvers up for future events is better, IMO.