This could be, but not limited to:
- Advertising
- Marketing
- League Fees
- Travel arrangements
- Stadium management
- Maintenance
- Training Ground/Stadium Lease
- Staff costs
- Local security
Unfortunately, the more successful your club is, the higher these fees get. One way to offset is thinning out player wages or hoping to get lucky with new sponsorship deals. Sponsors are the main source of revenue clubs use to pay non-footballing expenses (other than a filthy rich owner).
If you're concerned about new stadium costs, check your finance allocation to see what loan payments are made and what the costs of upgrading/rebuilding actually were. New stadiums create an immediate deficit in the short term but ultimately pay off in the long run. It's a huge investment.
One way I can see to cut costs is terminate unwanted or unneeded scouts. It costs money to send them to locales across the world or different countries to see matches and things. I normally have about 4-5 scouts only for a Premier League club. (1 for Champions League, 1 for Europa League, 1 for Reserves, 1 for U18s and one to send around central Europe or scout special events like the African Cup of Nations or the World Cup).