Buy a weekly option on a company it's going to announce a merger or predict any other many-sigma event with week/month-precision always using weekly options
Horse races are a thing for sure, funny you bring that out, a friend of mine actually owns shares of a trotter. He also posts pronostics on french races on horseturfpro.com
Edit: I just realized you need money to start gambling. Is OP asking about raising money without significant starting capital though?