I haven't done much travel writing recently, as the day job is too busy, but in the past I wrote 3 travel guides for a UK publisher. One on Florida, one on California, and one on the whole of the USA.
In general, if you can get an assignment first then "free" is easier. I had a letter from the publisher stating that I was writing 3 travel guides, and thanking everyone who read the letter in advance for any help they could provide.
So I spent a year travelling around the USA, getting free access even to places like Disney World, and VIP tours of film studios, and the occasional hotel or camp site thrown in (we travelled by motorhome most of the time).
Convention & Visitor Bureaus (Chambers of Commerce in smaller towns) have amazing access if you have the right intro or right pitch. If you are going anywhere as a travel writer, or even just writing from home, make friends with them and let them know what you are doing.
If they do get you a free hotel, resort, attraction ticket, meal then don't forget to thank them. Do it first with the venue (say what a great job the CVB did in pushing this wonderful venue to you, the travel writer) and then again back to the CVB thanking them for introducing such a fantastic venue.
Integrity is also important here, and when combined with hospitality then I always used to mention the venue if good. I always wrote a balanced review / article rather than an "over the top" praise which made it look like they were paying me to write it - that does neither party any good! And if the venue was bad then I would simply not mention them.
Enjoy your writing, keep your integrity, and stay friendly with the CVBs!!
