They are I guess you could say traditional parts of the liturgy, though they may lso have some Scriptural references.
Incense is a symbol of prayer, just as Moses was told (IIRC) to offer incense to God as a form of prayer. I think it is also mentioned in the psalms. It was used in the Jewish temple and throughout Christian history.
The bells are rung at particular important points in the prayer of consecration, to show their importance and to hold our attention.
In a larger sense, an important purpose of the liturgy is to prepare us spiritually and psychological to receive the Eucharist, and to offer praise and worship to God. It does that through the text, which gives us the doctrine and theology of what we are doing, but is also prepares us through appealing to the body as well as the mind - the eyes, ears, nose, even the way we move our bodies at different times in the liturgy.
This is because we are understood not only top be spirits, but creatures with bodies who need to incorporate the body into our worship. The liturgy is more effective if it can use all the tools on offer to help us to worship and receive God.