In this situation you do not want to work with a typical travel agency, what you want is called an online travel aggregator. OTA's are Travelocity, Expedia, Orbitz, Kayak, etc. For you to get a travel package on one of these sites, you need an application programming interface and distribution software. Basically you need the API, which is your specific xml codes and schema for booking the flight, trip, rental car, and renting gear, etc. There are tons of travel related API s on the web, here's a good site with some http://www.programmableweb.com/apis/directory/1?apicat=Travel
You build your website using the API. Then you need distribution software to get your website with your API to the OTA's. Sabre and Amadeus are some of the largest global distribution systems. Here's some others
You will need to essentially pitch your business plan to a GDS and if they see it as profitable, they will partner with you. OTA's will then basically pay the GDS for using your site and your APIs. You will then get a commission of that money from the GDS.
So that's a pretty brief rundown of how the tourism business works. Source: I'm a Recreation and Tourism/Business Major.