Do you use a travel day pack?

I just got home from a 2-month Central Europe trip and I brought a 50l pack and a draw string bag I got for free. I only used the draw string bag when I had a long day trip where I would put some snacks or lunch and maybe a rain jacket. The bag was typically uncomfortable, especially when carrying heavier objects like my nalgene bottle for water but it was nice because it weighs nothing and packs into nothing. The bag broke mid way through the trip which was somewhat expected but coming home and with my birthday coming up, I'm thinking of investing in a light weight day pack specific for travel. I think it would be helpful, especially when you travel on buses or planes and need to put your laptop or other valuables in it while your main bag is in the storage area. Does anyone use a day pack that is light weight and packs up nicely in your bag that they could recommend for traveling?