Is it all right to enclose a card from the store where the bride is registered in the bridal shower invitation?
Definitely. The shower really is a gift party; the whole point is to outfit the bride (ahem, the couple -- let's move into the 21st century here!) with stuff for the newlywed home. So yes, it's okay to insert those store cards about her registry into the invitations. The place where those cards don't belong is the wedding invitation.
Rehearsals + Brunches
The Bridal Shower