You need to think through how you pack – I suggest bags within bags, both to keep things dry and so that you can find stuff.
Then you need a system – things you won’t need today at the bottom (or middle if your bag has a zip at the bottom too). Heavy things should be near the middle of your bag, as that’s better for your back.
So, at the bottom you might have the food you won’t need that day, then your sleeping bag and mat. At the top you’ll need your waterproofs, first aid kit – and headtorch. It’s hard to find your headtorch once it’s got dark, and we wouldn’t get caught walking in the dark without a torch ( – well, not now we wouln’t, that’s the sort of mistake you only make once!!)
Think through what you’ll do when you arrive at the campsite. You might want to have some layers of clothing near the top of your bag, but make sure they are in a waterproof bag so you can pull them out without worrying if you’re putting up your tent in the rain.