If it's for a 'just in case' scenario, I would opt for the ready-made cartons. More than likely you'll have a good breastmilk stash anyway, and she honestly may not take to formula well now so might not drink much of it, so I probably wouldn't waste a whole bit package of it. Probably the cost will work out the same as the ready-made stuff is expensive, but if it's only for 5 days, for the ease of not having to make up bottles, I would go for the ready-made. Then it's just like your breastmilk in the sense whoever is staying with her just has to warm up a bottle a little rather than bottling the kettle, letting it cool, mixing the formula, cooling it to body temp, etc. I think I'd opt to spend a little more for the convenience given it's a temporary situation. At 8 months, if you're going to be mostly only formula feeding during the day, then I might opt for using the powder because you'll likely go through it faster (if you aren't also expressing) and use it up in time. Either way, definitely should still be first milk at that age and whatever brand you prefer. If you had one you used before and it didn't cause any problems, I'd be inclined to do that. As for mixing it, I'd just do a few trial runs to see what works better. Some babies won't take formula at all if they've been bf. Some will only take if mixed. My daughter wasn't a big eater either way, but she didn't have a preference. So I would just do a few trial runs before you go back to work and see what works best.
