When I was an internal auditor travelling weekly all over the United States, I had to keep track of all expenses so that I can be reimbursed. Similarly, business owners and employees who incur out of pocket costs associated with client service and/or business development should keep receipts and identify immediately the proper account the expense is related to. If you wait until you received the bank statement, AmEx bill, then you may not remember why or what the expenses are for.
To keep track while traveling, you can use an envelop to keep all paper receipts and write on the outside of the envelop your meals, hotel receipts, taxi, and miscellaneous travel expenses related to your trip. As you get a free moment (waiting at the airport or train station), you can enter these expenses into a Excel spreadsheet.
Also, while traveling you can also use your PDA to track expenses, but the envelope is still necessary to retain paper receipts.
If the expenses are not due to travel or not directly related to a client, then they may be general business development expenses. Even with these expenses, you must keep track and assign to the proper expense code.
Examples of business development expense codes:
Research & Development
Professional Development (Employee review lunch)
There may be more non-client related expense code since it depends on the business. Service companies should take extra heed at monitoring expenses because often their costs may seem intangible, but if you consider the cost-to-benefit of the expense, then you want to quantify it in order to manage cash flow more efffectively.