Backpack??

I am going for my first ever backpack style holiday with my coliks in end July. The main problem with this holiday is ..... I dun have one that can fit 7 days of holiday clothing (mine is just 20L tat I bought ages ago for light travel purposes). This is also because I am a person that love to travel in style & comfort with my hubby. So, shall I get a new backpack? Maybe I shall check it out at this great luggage place before I decide if I can just borrow 1....