Unless the bride & groom specifically request for no gifts to be purchased it is expected for a guest to bring one. Traditionally the bride & groom would not be living together until after they were married, so gifts were items for the couple’s marital home such as cutlery, ornaments & cookware. In recent times; many couples who marry are cohabiting prior to marriage and already own many of these "household items", thus changing the types of wedding gifts they receive.
Rather than letting their guests get creative with the gifts they purchase, it's quite normal now for a couple to issue a wedding gift list to their guests. The bride & groom will create a list of items that they would like to receive and the guests each buy an item from that list.
To prevent the same item being purchased by different guests usually the bride & groom will opt for one specific retailer/service, then as an item is purchased it automatically gets crossed off the wedding list. It's a very practical approach to gift buying as the bride & groom don't end up with unwanted gifts or one of those hideous looking ornaments from a relative (you know the aunty we're talking about!).
Alternatively, a common practice is to leave money or shopping vouchers in a card, this way the bride & groom can buy themselves whatever they like. Normally a particular retailer will be mentioned on the wedding gift list.
Another recent and fast growing gift idea at the moment is for guests to contribute towards a honeymoon, this is usually via an online service, a little bit like crowd funding for your own honeymoon.