Breastfeeding Question

J
What if I would like to go out for a day for an event without having to nurse in public? What's the best "prep" to have enough milk ready for my baby to feed from a bottle? and what can I do to prevent getting engorged? I went out for a small outing Saturday, and was completely overwhelmed with needing to pull over and nurse in the car for 40 mins every 2-3 hours. 😞