In My Hours you can enter expenses to every time log. It is also possible to directly attach invoices or other files to support the entered expense. Allowed file extensions are: .pdf, .csv, .xls, .xlsx, .doc, .docx, .txt, .jpg, .jpeg, .png, .gif.
If you need to enter only expenses without tracked time, such as an airplane ticket, you should create a time log of 0:00 duration and enter just the amount of expenses.
Additionally, you can also create a Tag (for example: 'Expenses') and mark all such logs with it. You will then be able to filter your Detailed report by this tag to quickly find such logs.