i suggest think twice...haha
i started off with a big bag...then the bag gets smaller and smaller...as i realise
2kg of camera equip with 1.5kg of tripod + 2kg of laptop and 0.5kg of water is no fun at all.
if you still want 1...i recommend kata bags...go to any cathay or penisular ...should have quite a lot of kata. bigger bags are priced abt 150.