The one item I would invest in is a good rain cover for your stroller (especially if using a double). If the stroller gets wet it is a lot more difficult to dry it out than to change your own clothes. Know where the baby care centers are and use them. They are the perfect place for a break and to pick up anything you forgot. Also the first aid center (or whatever its called) gave me cold medicine free of charge when I found myself at DHS with a raging head cold last winter. We pack very light - a few snacks, sunscreen, change of clothes, diapers, hand sanitizer - and leave a bag with the stroller. I will carry a small crossbody bag with my id, phone and a little cash as well.