35 litre is a nice size. I carried a 40litre on a thru-hike of the AT, but like Lori, my gear has evolved.

My regular day pack is probably about 10 or 12 litres, but it's jammed (I also carry enough to stay out if something goes wrong)

I've told the story here before, but early in my last thru-hike, a southbound hiker went by me and asked how far I was going. When I said Katadin, he looked at my pack and said, "but that is a day pack." Actually, it was partly in German, so the quote is not direct, but it was pretty funny.