Throwing The Garter
This ritual dates back to a time before woman wore hose with a garter belt. It was a chance for the single men to share in the good fortune of the groom. Today, it is believed that the man who catches the garter when it is thrown will be the next to marry. In the 14th century, is was customary for the bride to toss her garter to the men,  but sometimes the men got too drunk, and would become impatient and try to take the garter off her ahead of time. 

Tossing The Bridal Bouquet
Tossing of the bridal bouquet is a custom which has its roots in England. It was believed that the bride could pass along good fortune to others. In order to obtain this fortune, spectators would try to tear away pieces of the bride's clothing and flowers. In an attempt to get away, the bride would toss her bouquet into the crowd. Tradition says that the single women who catches the bouquet is the one who receives the bride's fortune and will marry next.

Loud Noises
Loud noises were said to chase away evil spirits, and during the ceremony, the guests would make  noises to keep the spirits away. Today, it's traditional that the bridal party honk their car horns while leaving the ceremony. 

Throwing Rice
The throwing of rice on the couple has always been symbolic of wishing
prosperity and good luck.  In the Orient, throwing rice means, "May you always have a full pantry."  Wheat and other grains are sometimes thrown in addition to rice, thereby also wishing prosperity and lack of want. Each shower bestows  "Goodwill Traditions" of  wealth upon the newlyweds. To this day, rice remains a token of a life of "plenty." 

Old Shoes 
The tradition of tying shoes to the back of the couple's car stems from Tudor times. Back then, guests would throw shoes at the bride and groom. If they or their carriage were hit, it meant good luck was bestowed upon them. In Anglo Saxon times, to establish his authority the groom symbolically struck the bride with a shoe. Brides would then throw a shoe at the bridesmaids to see who would marry next. Makes you appreciate the bouquet toss, doesn't it? 

Throwing old shoes after the bride is a sign that authority is being transferred from the bride's father to her new husband. A variation is for the bride's father to throw her shoe after the groom as a token of his surrender of his daughter.