In all cases of Raffle, Gambling or similar income you will want to consult with your accounting and legal advisers.
You will also want to review related IRS publications such as Publication 3079: https://www.irs.gov/pub/irs-pdf/p3079.pdf
To record raffle and other gaming income in the CRM use Other Items for Events (after the event is offline), or use the Invoice Item custom data set type option.
When using Other Items, be aware that this will make them available online if added before the event is over. Many states and jurisdictions have restrictions on online gaming and gambling.
As above, in all cases consult with your accounting or legal advisers for accurate details.