Backpack Suggetions?

I'm going to Thiruvananthapuram(trivandrum) for 4 days next month. I need a backpack to fit 3 days clothes +1 clothes for safety, And a space for water bottle, medicine and extra space left over to put anything I buy there in it(a lot). I need it to be comfortable. I was thinking about the safari seek 45l backpack. Thank you.