Depends what I'm doing. Close to home? Libre reader, nothing else. Out for a walk or run or cycle? Food gets added as a minimum - normally jelly babies + a few biscuits (clubs or similar). Quantity depending on length of trip - 4 for an hour, more for longer. For a longer trip cycling or walking I'll carry my insulin pen, but rarely use it unless it coincides with when I want to take my levemir (and I'll have two with me if that's the case). If I think I'll need money, I'll have my finger prick meter with me, since it doubles as my wallet. Overnight I'll have a pot (old pasta sauce plastic pot, jam jar sized) with spare vials, more needles, miaomiao (I only wear that at night) and tape.
How to carry?
I'm less good at that. If going minimalist eg running, pockets + a belt pouch works. Otherwise I tend to go for a bag of some kind (rucksack, barbag), with the various bits carried loose in that. I do have a little bit of a gap in my setup for shorter walks where I don't need a bag - in winter it's easy, the coat has enough pockets, but shorts pockets aren't enough for summer.
I don't have any formal diabetic bag though. The nearest is the pot of little things.