Styrax benzoin: A clearing agent and a means of making spirit manifest, Benzoin is an appropriate offertory material and its profoundly beneficial. Use this when you're seeking clarity & wish to elevate your ritual work. When working with this, let your mind follow the smoke and its undulations, as this can provide the means through which deeper states of meditation can be reached.
Protium copal: A consecrating agent and means through which self-work can be done. Mixing copal with your blood before placing it on a coal can be an incredibly beneficial means of connecting with our roots. In the context of Serpent Sorcery, when burning this, make a point of feeling the smoke envelop you as though it is a living serpent, as that forms the basis of deeper initiation within this Work.
Daemonorops draco: Also called Dragon's Blood, this is a specific variety, and in this case the name of the source of this resin is exceedingly important for reasons discussed elsewhere. In this form, this is both an offering to the Earth and a means of empowering your spellwork. If you use this with the intention of connecting to Serpent Spirits, you'll find that this both wreathes you in their energy and allows for visionary work to remedy internal issues & engage in self-development. This can, when used correctly, inspire the spirits you work with to engage with you in a more active way, allowing for greater external results to occur.
Pinus rigida: Pitch from this tree in particular is quite useful in spirit work of all kinds, and when used in conjunction with Serpent Sorcery, this acts as a binding agent and a means of making these entities more manifest. This is an additive rather than being a sole-operator in magic, so I would strongly suggest mixing this with the above. For instance, when used with Protium copal, the smoke is made holier by comparison and has an aspect of conveyance that increases the throughput of any prayers.
Experiment with these. There's a lot more options out there, but these are often easy to procure.