https://www.mathworks.com/help/daq/log-analog-input-data-to-a-file-using-ni-devices.html shows an example of logging to a file.
That particular example shows plotting after everything is done, but the code could easily have been changed to plot as you are going.
The basic idea is to fwrite the data as it comes in, and after everything is done, read it back from the file.
If you happen to have a situation where you can set a strict upper bound on the number of samples to be read in, and all of the samples will fit in memory, then instead of writing to the file, you can pre-allocate space for the maximum possible number of samples and have the callback function assign into that array. Do not use
samples = [samples, newsamples]
or
samples(end+1) = newsample;
because doing that forces a lot of data copying that will slow the system down too much.
If there is a reason why you cannot allocate the full buffer right at the beginning, but you are still sure that you have implemented an upper limit, then at the very least avoid re-allocating too much. For example you could allocate a cell array, and you could put a megabyte's worth of samples into each cell location; that would avoid allocating a lot of memory at one time and yet not have to rewrite memory in any array.
