I have a 3 month old daughter and am currently planning a short camping trip next month here in Australia where the weather should be warm but may also be wet. What should I take to ensure an enjoyable and safe trip? I'll only be in a national park somewhere not too far from a car and that won't be more than an hour's drive from civilisation.
This question is specific but it should probably be edited into and answered as something more general.
I have taken my kids camping since they were just a little older than that, and the only things I would plan to take over and above a usual trip out (with the usual nappies, wipes, water bottles, spare clothes etc) are:
lots of spare clothes. LOTS! Both for when they end up in mud somehow, and also for adding layers - they can't cope with temperature changes as well as adults. When it is cold, wrap them well and check their extremities regularly. When hot, take shelter.
lots of water. While wipes are essential, you will find you need more water than usual. If camping for a few days, it is useful to be able to boil clean water at every stop to help sterilise items.
blanket/toy/whatever they like to cuddle. These things get lost. Take spares - it will make your life easier.
If you're breastfeeding then you don't have to worry about food. Your child will need something to sleep in, we've used everything from a car seat liner to a sleeping bag folded in half, but the best is probably one of those sleeping bag style jumps that have should straps.
A hat is always a good thing to bring one with a chin strap, as is a source of shade (tarp, beach umbrella, etc.) if there is no natural shade, but since your child is only 3-4 months old a blanket over a removable car seat is probably fine.
For carrying the child, I couldn't recommend anything better than an Ergo Baby, we first used ours when our son was 3 months old, and he slept the whole time he was carried. It feels great carrying them that way, and they are close and warm, although they look like a spatchcocked chicken when you peel them off your chest.
At that age you don't need much more. Lots of garbage bags to wrap up dirty diapers, it's worth learning how to knot off the bag after each diaper so that you can put about 5 diapers in a bag without the smell escaping (much).
If you aren't in the habit of spending 12-16 hours a day outside then there are quite a few things that you might forget to bring:
Some babies sleep happily in a tent, especially if they've nursed off to sleep. And some don't. The more things you bring that are familiar (blanket, stuffed animals, the pad from the bottom of the playpen, the windup mobile that plays a lullaby) the more likely going to sleep will work. (Our Moses basket worked well for us because it was something we could easily bring.) Naps are problematic because you just can't make a tent dark. Perhaps bringing a stroller so you can walk the baby to sleep might work. Our babies loved to nap in the canoe.
Books to read if that's part of your evenings now. Your baby monitor if both parts are battery operated. Something to help you carry the baby on a beach or a trail or somewhere else wheels are not going to work - a sling or a baby pack or the like.
Your camera. Outdoor babies are generally happy babies, and having a child with you lets you see how amazing it is to say, put your feet in the water or run your hand through sand. Let go of whatever you normally do all day because nothing pulls you into the moment like being outside with a child. You have to keep them from eating dirt, drowning, crawling into the fire ring, and the like. And on balance, that turns out to be a great way to spend a day!
The Great Outdoors!