Offering live beings to the Gods is extremely disrespectful! All life is sacred to the Gods and hurting another human being or animal will only make them look down on you with pity. If someone killed and offered another human being to you, would you accept it or would you find the behaviour psychopathic?
This is a great offering. Its a way of you telling the Gods that you welcome them to your home. Gods do not force themselves upon anyone. Also, all Gods have their personal favourite incense smell and they will appreciate it if you go out of your way to find it. If not, anything that smells good to you, they will like it too.
Candles are our way of communicating with the Gods. All of them have their specific candle colour while communicating with them. When you offer a candle to a god, they will associate their energy with that candle and whenever you light that, it will be easier for you to reach them.
(White candles are associated with Christianity and Abrahamic religions. Some Gods will refuse the offering. It is strongly recommended to not offer a white candle)
You can make a tattoo of your guardian's sigil or a symbolic meaning of them.
Gods always enjoy the personal touch. It is always impressing and emotionally important to them if you put your time in to a project.
If you paint, do a painting for them! If you are musician, write them a song! If you cook, cook them a meal! Whatever you are good at, you can use that skill to fashion your offering. They will appreciate it greatly.