The fact that you can open up a market for their products, or give them some positive publicity, or make life easier for their employees, or help guarantee a literate workforce, or eliminate problems caused by drugs, alcohol, or domestic violence is meaningful to a corporation. Many corporations make non-monetary contributions, which are often easier to get than cash. Corporations will often give their old desks, filing cabinets, computers and computer tables, chairs, and so forth. If you see a corporation redecorating, ask them what they are doing with their old stuff. They may be more than happy to have you haul it away.
Some corporations donate the products they produce.
Food and beverages are often free to special events, but more expensive equipment can also be obtained. They can loan you their staff. Supposing your organization is a complete mess in terms of your accounts. Advertising, public relations, design, management, personnel, and training are some of the staff corporations can loan you. These loans can last for days or weeks, or with some corporations up to a year.