Get the kid a small back pack. (School book bag will work). Let him carry his own water bottle, extra gloves(two pairs), and extra socks (for when he steps in the wet puddles). Keep it to that only so there is no real weight to tire the kid out. You carry the snacks, and they will also be needed to keep him happy when his little stomach says he's hungry. With water, snacks, dry gloves, and dry socks, you can keep a kid out for a long time. Dry, warm, and interested, and they are happy.
From and old Dad that went through this not all that long ago.