How many passengers can an Airbus A380 carry?
Wikipedia lists three basic configurations for the A380-800:


407-526 (3-class)
644 (2-class)
853 (1-class)


However, different airlines have different configurations. The lowest number of seats is Korean Air, with 407. The highest number of seats is Air France, with 538. Emirates has discussed plans for a configuration with 644 seats but it does not appear on the list (or on SeatGuru).

As far as baggage, this thread states that the A380-800 might carry 19 LD-3 containers of baggage, or 3002 cubic feet, which is for about 471 passengers. The bulk hold, which is for loose baggage, can hold 1,525 kg or 14.2 cubic metres (501.5 cubic feet), and the A380-800 can carry 8,000 kg of cargo in addition to a full passenger load according to Emirates.

An average suitcase is about 0.1 cubic meters in volume. If the bulk hold is 14.2 cubic meters, then it could theoretically fit 142 suitcases. But an average suitcase weighs 50 lb, so 142 suitcases would weigh 3220 kg, which is over twice the weight capacity.

The LD-3 containers add an additional 85 cubic meters of space, or 850 bags. This is a total of 942 bags, which for around 500 passengers sounds very reasonable.

But wait, there's more! What if the rest of the cargo capacity was filled with luggage?

Emirates above claims a total of 12 PMC and 44 AKE of cargo capacity. The properties are as follows:


PMC

23 cubic meters (max)
6700 kg capacity

AKE

4.3 cubic meters
1497 kg capacity



This is a total of 465.2 cubic meters of capacity, or 4652 suitcases, or 105,505 kg. The containers could hold a maximum of 146,268 kg.

So the bulk plus container capacity is 4794 bags by volume. This is assuming every container could be packed completely full of bags with a density of 227 kg/cu m, so the actual numbers would probably be lower.