pad limit
If the chip is pad limited, you can do the following:
1. See if you can reduce the width of any data busses. One way to do this is to half the size of the bus and double its speed, so that the bandwidth is maintained.
2. See if some of the pins can be shared. These pins will have dual functionality, which can be configured by the chip.
3. See if flip-chip packaging is feasible, that way you can put mulitple rows of pads on each side.
4. Add your name and photo on the white spaces in the chip
If the chip is core limited, you can do the following:
1. Remove any redundant/unused logic
2. Consider removing some functions that are not important
3. Move to a smaller technology
Of course, if you don't care about die size, you can simply grow the chip size without worrying about any of the above.