Thank you. I've a speciality pack for photography gear (with compartments & extra padding) and not planning to use the day pack for same purpose. Most likely, my wife will carry the day pack.
It sounds like, from your suggestion, that I should either go for a school bag or a 50L pack. I wasn't sure if carrying a scantily loaded big pack was worthwhile and was concentrating on small packs like the ones in OP (<25L). But I might be missing something because until yesterday, I had no idea about hiking gear and I can't say in one day I've gained a lot of knowledge.

P.S: I am not getting email notifications of replies posted. What do I need to do to get those?