First place goes to my windows XP pro dell dimension 8400 it's now over 9 years old, has never needed an OS wipe and the only item I have replaced is one hard drive after the original started clicking after 8 years. It was an upgrade at that point though as I went from a 520 gig to a 1.5 terabyte drive.
Second place goes to my 13 year old 19" monitor.
Those two items have been with me long before digital photography via the use of scanners and moved right along with me when digital came into focus for me. They have done me proud.
Edit: Oh the cost of the PC (refurbished from Dell) was around $900 and the 19" monitor was around $750 way back then.
Edit: Fokker While I have not had my backpack but 3 years. I have to agree with you on you statements. In my case mine was free so It really paid off. My original camera bag sits collecting dust now. Very good answer!