Quick tip - I've been a Franklin-Covey user for many years now. I might not have survived college without it faithfully by my side. I learned through their training to use the priority method of assigning things based on have to, need to, want to, or whichever terms you would like to apply. I then go through and assign a number to each of those tasks and work through them in order. Aaah, chaos controlled...
Well it has been driving me crazy that although I could use categories in Outlook or the priority field to group my tasks, I had no way to assign a custom rank. Neither start date, due date, nor alphabetical order is always the best sorting method. I prefer to do it the hard way I guess.
With the help of a specialist on my team I found how to add a custom column. Actually quite easy. First, collapse any tasks you have in the to-do bar and right-click within the white space and select Properties. You should have no problem on your own clicking Fields and then creating a new custom property. I chose to call mine "order" The tricky part is how to have the column appear in the to-do bar.
Click on Other Settings and then look for the field below. Uncheck the box to use compact layout and select the radio button for "Always use single-layout". You will then be able to customize which columns appear on your to-do list. Unfortunately, if you resize the to-do bar your columns will adjust widths so you may need to break one habit in sacrifice for another.