I make sure to communicate to T when I'm dissociating.
Grounding techniques can be really effective. Glad the cold Coke can helps bring you back. Ice packs are great, if your T has those. Sometimes I bring really cold, or really warm, tea in a thermos to maintain the temperature. I bring tea with an aroma and taste that feel comforting to me. Other things I've found helpful: taking deep breaths to the count of 4, or 5, while trying to relax the muscles of my face and soften my gaze (I get the deer-in-the-headlights feeling, and it feels like my mind is stuck in partial oblivion); wiggling my toes and feeling them touch the insides of my shoes; sensing the floor beneath my feet, and the chair/couch beneath me. If these don't work, sometimes I will bend forward with my head upside-down, and stay there inside my "safe cave" for 10-20 seconds, then come back up and stretch my arms wide... might be contraindicated for those with blood pressure issues, though. Dissociation is so frustrating, especially during EMDR. Sometimes it helps if I find gratitude for the dissociation - it's trying to protect me - so I (deeper, core self) thank it for its intention, remind myself that I'm safe right now, and imagine it dissipating like a cloud.