Is there possible that current block do not have uncles? As we know that Main block contain the contract information , What does uncles holds ?
Is there possible that current block do not have uncles?
A block may or may not contain any uncles. Specifically, a block in the main chain can contain a pointer to a list of one or more uncles. The rate of uncle/ommer creation - i.e. how often creation happens - is covered here: What is the significance of uncle rate?
As we know that Main block contain the contract information...
It contains a hash to the root of the state data tree. Strictly speaking the block itself doesn't contain the contract data, it just points to it.
What does uncles holds ?
Uncle blocks hold the same data as normal blocks (e.g. transactions, which themselves bring about changes in the state data), it's just that this information didn't manage to get into the canonical main chain in time. It is no less valid though. See What is an uncle/ommer block?