Modak is a sweet which is a favourite of Lord Ganesha. It has a special significance on Ganesh Chaturthi Puja. In the ceremony one must make an offering of twenty one modaks to the deity.
Pic Courtesy: Wikipedia
Incense Sticks and Lamp
The incense is a fragrant offering to Lord Ganesha. The fragrance is supposed to be pleasing to God, and has a purifying effect.The lamp bestows light and drives away the negative aura around the the puja premises.
21 Blades of Kusha/Durva Grass
It is a symbol of prosperity for its propensity of regeneration. The grass signifies renewal, rebirth and fertility which Lord Ganesh also stands for.
Mouli - Red Thread
Mouli or Kalawa is a cotton red thread which is very sacred. The thread is used as an offering of cloth to the deity. The thread is tied around a kalash. Mouli is used in almost all Hindu sacred rituals.
Kumkum and Sandalwood
Sindoor or kumkum is used for Ganesh pujan for purification and protection and enhances the inner eye. Sandalwood is known for its aroma and cooling effect and is generally applied to the forehead of Ganesha.
Supari - Betel Nut
Supari or Betel nut is symbolises the ego that one must offer to gods, thereby leaving only the soft, pure qualities. It signifies our desire to receive blessings without ego.
Also known as Shreefal - every part of coconut is useful in some way or the other. In Ganesh Pujan, it signifies the presence of Shiva, and is supposed to attract all the blessings from heaven. Breaking the coconut signifies breaking the hurdles in life and Ganesha - Vighna Vinayak is worshiped for the exact same reason.
Red Coloured flowers are the favourite of Ganesha. Red hibiscus is offered to the deity as the flower is radiant and has a pleasant fragrance. Fresh flowers signify beauty, purity, softness and fragrance.