Andy
Thats a nice little sporran in the link you posted - they make great possibles bags and you can often find them over here in second hand or charity shops.
What do people keep in them? Well if I'm wearing one it's cos I'm all dressed up to go out to a wedding or similar so I'll have some money and my car keys - nothing exciting I'm afraid. However in the old days they would have been used exactly like a possibles bag - an everyday sporran would probably have been bigger than current dress sporrans and would often have been slung to the side, you cant walk too well with a heavy bag slung the way Maddave's picture shows.
FYI it is considered the height of bad manners not to turn your sporran to the side if you are dancing with a lady - looking at the size of maddaves you can understand why!
George