Marketing and networking efforts
Professional training or conferences for the staff
Improving office facilities, computer hardware, etc
Spending some budget (hours) on process development, sharpening the saw.
Reinvesting typically implies growth, so I'd say its some combination of improving the efficiency of current staff and/or bringing on more staff, and bringing on more customers.
Some small things:
- an online timesheet service
- a nicer office including furniture or a reception area
- out of town conferences for staff
- upgraded analysis software
- a nice holiday party
- more references, maybe in areas which are adjacent to your current area
- learn about new things, like CLT or kinetic structures
- an online file management system like egnyte etc.
- send out some marketing materials like postcards