Power a 12V 30A (instantaneous) load. Possible with 18650 cells?
Li-Ion cells designed for use in power tools are capable of that kind of current - easily.  Laptop cells usually are NOT designed for that use.  Doesn't mean that they can't supply that kind of current, just that the cells might get hot and will most likely have a short lifetime.

However, put several cells in parallel, then put the groups of parallel cells in series and now you have something usable.

Nominal cell voltage is about 3.6V or 3.7V.  Three cells in series is about 10.8V, 4 cells in series is about 14.4V.  Personally, I'd lean in the direction of using the higher voltage (4 groups in series rather than 3).  

If you use 16 cells as four series groups of four cells each, you should have no problem with either getting that amount of current OR short lifetime.

If you really have a lot of cells available, make the parallel groups more than four cells each.  

One final note: putting multiple cells in parallel helps if you have some cells that have higher internal resistance than the rest.  The load is spread amongst all the cells.