I see lot of people offering flowers, fruits and other tangible things to god to please him. However, I fail to understand, how can god be pleased by offerings that are his own creation.
I would say, its a matter of love. Imagine your 1.5 year old kid(actually I have one now) grabbing some stuff from your plate as you are eating and feeding back to you and showing his tiny teeth. How to you feel? The Supreme Lord is a person. And so is other gods as well. And everyone wants sweet relationships. And one of the ways by which relationships are realized is by offering and accepting stuff, be it fruits or flowers. Hope this helps.
God or Iswara is not gaining anything ,we offer him fruits, flowers and leaves because it pleases us.God doesn't need them so to speak ,as he is the creator and owner of all that exists.Its because of our love and devotion that we offer him such meagre things.
When we say "naivedyam nivedayami" during a shodasa upachara Puja it doesn't mean that we are literally feeding him but it means that we are making him know that we are aware of the fact that its him who have created all this and hence we can only partake the food after its being offered to him.
Btw,a question such as this never appears(or it should not appear) in a devotee's mind.
EDIT-Refer also to the Dasopadesam(the ten commandments) given by Paramacharya Maha Swamigal JagadGuru Shri Chandrasekarendra Saraswati .One of which says:
Upadesam # 2) Man by himself cannot create even a blade of grass. We will be guilty of gross ingratitude if we do not offer first to God what we eat or wear - only the best and choicest should be offered to Him.
This Upadesa nicely address the question you have asked.
The best answer to your question is, to show respect. We offer them food/sweets right in the beginning without it being "jhoota".This is purely in the sense of respect.
Also flowers are a part of the offering because of their incense.