Here are some important utilities that you should always ready to be user:
1. WireShark: http://www.wireshark.org/ to sniff and analyze any kind of data in your lan
2. Sysinterlal: http://technet.microsoft.com/en-us/sysinternals/default.aspx
and
Sysinternal Live: http://live.sysinternals.com/
Process Explorer Task Manager enanchment
RootkitRevealer
Contig, command line defragmenter utility
3. Unlocker: http://www.emptyloop.com/unlocker/ Unlock used file and Directory
4. Wipe utility: http://www.dban.org/
5. Tree size portable(and similar utilities http://www.alessandromazzanti.com/2013/02/manutenzione-programmi-per-trovare-le.html and http://www.alessandromazzanti.com/2012/09/programma-treesize-avere-la-dimensione.html) or WinDirStat: http://windirstat.info/
