GMail's search feature is not that great, because it cannot find mails if only the beginning of a word matches the search query. So if you search for travel then it won't find mails with the word travels.
This is very annoying and makes searching much less useful than it could be.
Luckily, there is a solution. You should index your mail with a different tool which can do these kinds of searches. One such tool is the Opera Browser which has a very capable mail client in it. Don't worry, you don't have to use Opera for browsing if you don't want to (though, it's a great browser). You can use it for GMail search only.
Here you can read about setting up Opera's mail client for GMail and make sure you set up it so that Opera only copies the mails from GMail, but leaves the originals there (probably this is the default). When you are done Opera will start copying the mails which may take some time if you have lots of emails.
When it is done then you can start searching your messages with the Opera Mail client and it will find words even if the search matches only the beginning of the word not the whole word.
Just open the Mail panel and click on the Unread view, for example, and in the top right corner there is the search box.