I make up about 3 bottles in advance. I sterilise 6 bottles, make up three and store 3 bottles for later (with lids on etc so I only have to sterilise once a day). When making up my bottles I boil the water and leave to cool for no longer than 30 mins (usually about 10), make up the bottles, rapid cool in a sink of very cold water and then store in the fridge. When I need a bottle I microwave to warm (I used to use a bottle warmer but know many people who microwave and it has been fine - just need to shake the bottle really well. I usually shake, test temp on back of wrist, shake and test a second time to be sure).
I do know people who use cooled boiled water and store this at the back of the fridge and then add powder and warm when needed but I was of the understanding that you need to make up with boiled water around the 70c mark to kill off any bacteria in the non sterile powder. But I guess either way is a compromise to making them up fresh.
When out and about I either keep a made up bottle in a bottle warmer (if I know she will need a feed within 2 hrs) or if I am out for longer and she is likely to not need a feed within 2 hrs I use the premade formula.
I use SMA.