In reply to lizziecaplan:
Hi Lizzie, Myself and a mate did exactly the same thing last year.
We dropped off some re-supplies including bivvy bag, stove etc in the trees just off the A5, on the ascent to Pen Yr Ole Wen. We then drove to the Vaynol arms (Pub down the road from Pen Y Pass). We spoke to the landlord and he agreed to allow us to leave our vehicle in their carpark for a few days. If he'd said no we'd have left it opposite in the campsite.
Friday night we had a beer each and some food then got a taxi from the Vaynol to Pen Y Pass carrying a different bivvy bag and stove. Walked up the miner's path and bivvied on the top of Snowdon.
Started the walk at 05:30, dropped off our 1st night bivvy stuff on the way past the Vaynol after descending from the 1st 3 peaks. We then carried lightweight sacks until we came down from Tryfan. Walked up the A5, grabbed our bivvy stuff and shoved that into our rucksacks then continued up the Carneddau. (Heavy sack again but you're nearly there)
On the 3rd to last peak Foel Grach there is an emergency bivvy shelter. You're not supposed to plan to use it but we found it very handy in that we dumped our bags in it, topped out on the last two peaks then walked back to the shelter and accidently slept there the night.
Next morning we had to walk back to the A5 and got a bus back to the Vaynol.
Very successful 15 peaks mission
Post edited at 11:33