I’m going on a backpacking trip around SEA at the end of the year and I need to choose a good backpack.

I want something I can take as a carry on so I’m looking at a 40L one. Just wondering if this will be big enough?

I also noticed most backpacks come in mens and womens. Can someone tell me what the difference is and if any women have purchased a mens bacpack did you have any issues?

Thank you!!