3 chemicals to produce light
As discussed in the comments... The two component chemiluminescence reaction:
(Solution 1) To 50 ml of deionized water add 10-50 mg of luminol, 10-20 ml of 10% ammonia solution and 1-5 ml of 3% hydrogen peroxide. (Solution 2) To 100 ml of deionized water add few milligrams of copper salt (e.g., sulfate) or few drops of blood or fresh horseradish juice. These are approximate quantities (they should work), but you can experiment with the concentrations, after all experimenting is the most fun part of chemistry. Now take the solution 2 (whole) and add few milliliters of solution 1 to it and shake it. You should be able to observe a faint glow. A brighter emission requires organic solvents (DMSO, DMF) and corrosive chemicals (KOH). Adding a third liquid that will separate the two other (as the OP suggested) is not a simple thing to do. I would do this otherwise: add some neutral ingredient to solution 2 to increase its density (possibly sugar, but I'm not sure if that will not quench the chemiluminescence) and place the solution in a container (preferably a long tube). Then carefully pour the solution 1 on the surface of the solution 2 (so that the solutions won't mix). When you shake the container the solutions will mix and produce glow. Another idea: place one solution in a container and layer it with a hot paraffin from a candle and allow it to cool down. Then you can pour the second solution on the solid paraffin. To start the reaction, simply break the thin paraffin layer by shaking (you can place some glass marbles in the container).