Handbag/Sidebag?

Hey im about to travel on holiday with Emirates, and it's my first time so first of all id like to ask everybody for some advice and tips and hints on travelling. The main agenda is that, the aeroplane allows you a sidebag, i had in mind to take a messenger bag like a adidas one here>>http://www.argos.co.uk/static/Product/partNumber/2861845/Trail/searchtext%3EADIDAS+MESSENGER+BAG.htm. would this count? if not please give me a link or recommend what would count.