Tips on building a stash

Hey there, been breastfeeding my boy for three weeks now. I pump 1-2 times a day and catch what I can with a haaka through the day. We bottle feed before bed and sometimes when my husband is around so I can get a break for a nap here and there. We have anywhere from 4-9oz in the fridge at any given time which is about 2-3 feeds worth. However, I’d love to start being able to freeze some here and there so if I want a night away, there’s a bit more of a buffer as I know my son can easily power through what’s in the fridge within a few hours if he’s in a cluster feeding mood. Any tips on how to start doing this? I’ve had it happen a few times that I pump after a feeding and my son wakes up shortly after and wants more but then gets frustrated when I don’t have enough milk because I just pumped. so I end up having to feed him what I just pumped which seems like a big waste of time since I’d way rather just feed him at the breast than pump for 15 min and then have to bottle feed him. It’s still early and we’re still getting into the rhythm of things so just looking for tips on what works for others.