Yes, powers of 2 used most often. You get an average of 75% fill with powers of 2. If a higher fill is desired you can use a lower exponent, like multiplying the size with 1,5 each time.

Resizing exponentially works better than with fixed blocks in many cases, because with fixed blocks, you can run out of memory again simply by increasing the amount of items. To prevent this you need to make the block size very large, which means you get a very low efficiency if the count is low. However, if the amount of items can be estimated well, fixed blocks can be better.