I like Mathematica, Magma and Maple but I use PARI-GP, Sage, Perl and GCC because they are free software.
Because I am interested in knowing low level details about computing systems I find it sometimes important to know the exact configuration of bits in data files and streams. For this reason I find hexadecimal dump programs like xxd (xxd-1.10.tar.gz) invaluable because it has a switch to reverse the process and producing a binary file from a dump. This is something that the utilities "od" or "hexdump" are not able to do. The "xxd" program is included with a "Vim" installation, but vim is not always installed. Note that "xxd" does not handle Intel or Motorola hex file formats. See also a similar dump/restore program xd by John Walker at Fourmilab.
Another important detail is validating plain ASCII text files. For this reason, I wrote a "C" program "picky" to find and report on deviations from strict plain ASCII text file definition. As far as I know, there is no other utility program that can do this.