However , some sealed packs of cards can still be quite valuable , and complete sets of cards featuring the Nationals can be great collectors ' items .
Possible exceptions to this include trading cards , as their contents are not known until the pack is opened .
Some sealed packs of cards can still be quite valuable , and complete sets of cards featuring the Nationals can be great collectors ' items .
Possible exceptions to this include trading cards , as their contents are not known until the pack is opened .