Weddings are very special days in the lives of everyone so blessed to have them, and consequently, they deserve special attention when it comes to planning the music. But it is not so simple as merely picking your favorite songs because it's "your day". There are many important considerations, but first among them is that weddings (whether as a part of, or outside of holy Mass) constitute a public liturgical sacrament. Consequently, all the rules governing music at Mass broadly apply to weddings as well.
What does this mean? Practically speaking, weddings are not a case of simply getting everything that you want. For instance, secular songs which may be meaningful to a bride and groom (and that may even be somewhat religious in theme) are inadmissible to formal public liturgies. True, authentic liturgical music / hymnody is to be used. If there are songs that are particularly meaningful to the couple, wedding receptions are more appropriate places to feature these songs. On some occasions, they may be worked in as prelude music, but solely at the discretion of the Director of Sacred Music (hereafter DoSM).