backing up selected tables in a database
The smallest for of a BACKUP DATABASE can only be a filegroup.  So in other words, if your tables are all confined to a selective filegroup you could achieve your goal through backing up that filegroup.

But I'm guessing that you probably don't have all of your backup-desirable tables in one filegroup isolated from the rest.  In which case you'll have to get a little creative.

What I'd do is just script out your desired tables.  You can do this by right-clicking your database and selecting generate scripts.  Walking through that wizard you can select the specific database objects to script out.  You can also set the option to back up both schema and data.