In Firefox you can right-click on a site's search box and "Add a Keyword for this Search...". In Chrome you can manually add search engines and assign keywords. In Orion you can bookmark a URL and insert a query variable.
DuckDuckGo bangs are decent, but I don't like that it has to hit duckduckgo.com first (please feel free to criticize this preference). And while I've only used a handful of DDG bangs, the AirBnb one is not as good as the URL I extracted myself.
I'm wondering why it's not easier to configure browsers to send queries directly to a site's own search engine.