My sister has a couple of God children and this weekend she was Super God Mommy to cute little Mackenzie aka Izzy who is 3 months (I think...lmbo). Well while she was her she let me know that Izzy's Mommy sent her pretty unprepared. My sister is a jokster and asked me if there was a book that Izzy's Mommy could read so she would know all this basic stuff...I am sure that there is one some where, but I will take a page out of my mommy manual ind list some ESSENTIAL diaper bag items.
First of all you need a diaper bag that you can fit everything into. I have a tote from Pottery Barn Kids that I absolutely LOVE. They don't carry mine anymore, but Land's End has one that is similar. What I was looking for was something deep and wide. Most diaper bags come with a changing pad that matches the bag...but if it doesn't you can buy one or buy disposable ones, I recommend just buying a reusable one. And most reusable ones come in a set with a diaper carrier (which is another essential) that you will definitely need to hold your diapers. Every brand of wipes also makes a travel size that you can refill. So don't just keep purchasing them...just refill them with wipes that you have at home!!!!
I would also recommend that your diaper bag be able to hold your bottle cooler. I personally LOVE the Similac Travel Cooler that came with my welcome pack at the hospital....so much so that I bought a second one!!! It is the PERFECT size for a diaper bag and it holds and keeps cold two bottles all day!!!! An item that I bought just because it sounded like a good idea was a "wet bag" that is used JUST for putting soiled clothes in. And BOY has it come in handy. I LOVE LOVE LOVE this item.
You of course want you diaper bag to be able to also hold a change of clothes for your baby. With Aiden I would have 1 full outfit change (including socks) and then just a onesie. That way if he has to be changed more than once I would put him in the full outfit the first time and hope that it is close to the end of the day when he needs the second and I can put him in just the onesie. Or if we end up being gone all day and don't get home until after bedtime I can put him in a onesie where ever we are (because that is what he sleeps in) and put him to bed per usual.
Some extras that you would want is room for toys, a pacifier carrier, snacks, diaper rash ointment (personally like Butt Paste), or some baggies that you can put stinky diapers in. I personally don't carry a purse anymore...lol...so I have my wallet in the diaper bag as well.
These are what I would think are the essential diaper bag items...ESPECIALLY when someone else is taking care of your baby. I have also left instructions or Aiden's schedule in his bag when someone is taking care of him for the first time...even the first time my mom kept Aiden over night...lol. No one will know your baby like you do so it is your job to make sure the person caring for him/her knows as much as possible so your baby stays a happy baby!!!!!