International Rescue/Superhero!
This one requires some charitable donations, but I'm sure the UN could help out here. At the same time you will need to jeep check on your ego in case it gets too large so a degree of anonymity may be required (probably not a suit where you look like a bat or spandex based however).
You have pretty much the ultimate logisitical tool. Instantly able to transport matter from point a, to point b. Anywhere.
You start off by announcing to the world at a press conference you have this technology and this is how you prepare to use it, so everyone knows about it, and makes it harder for anyone else to try steal it or coerce you into a different train of action. Include a demonstration plus details of your charitable donation and how people/organisations/business can help.
Next. Portal transport, using your stockpile of charitable donations you buy yourselfs a quick and handy transport option. Something like a transport place which can take a helicopter and/or you can skydive out of (face it you're going to want to make an entrace where you can!). (Somewhat like Thunderbird 2 I suppose.)
Second thing. Hire a team to monitor the world (space station optional), they keep track of all news stories around the globe allowing you to respond.
Third thing. Base of operations, you'll probably want to stockpile resources for distribution and a place to service and fuel your transport.
Finally save the world!
* Drought in Africa. 500
Fly one portal under the Niagra falls, the other to Africa, water quickly appears, use it to top up a reservoir (somewhat ambitious) or attach to the back of your transport vessel and water the ground below.
* Volcano in the pacific. Use it to evacuate people away from the danger, where they instantly walk from the impending lava straight into a camp with fresh linen and running water.
* Food crisis in Sweden. You set up one portal at your base of operations (or place managing aid), and the other where the food crisis is. Instant delivery of supplies without the logistical worry (think how long it takes to load and send a plane, plus logisitcal cost of crew, fuel, maintenence etc).
* Disease outbreak in Australia. Why worry about multiple plane/ship journeys taking people and medical supplies when you can just send them through the portal.
* Miners stuck down a deep mine in Greenland. Ok you still have the trouble of getting down there and back yourself, but whats one trip compared to multiple especially if theres a lack of supplies.
There are so many endless possibilities of how you could save the world, cutting down on cost and environmental impact (your own plane journey compared to multiple hercules). You're not being paid for it, rely on charitable donations and will try to help anyone anywhere wherever you can, however the multiple inspiring real world heroes you hear on the news become one (hence keeping your ego in check).
And I leave you with this. Where there's heroes. There's always villians. People will try obtain this technology from you for their own evil gains. 500