You must get a decongestant and antihistamine combined drug. A good one, the kind that is kept behind the pharmacy counter now, but still considered over the counter. Also buy afrin. The risk is the congestion, inflammation and pressure in your ears can burst an eardrum. It can also be painful to fly, especially when descending, but again the biggest thing you want to avoid is damaging your ear. Especially if you are connecting, the second landing, when already uncomfortable can be really uncomfortable.
I recommend against cold and flu meds that include cough medicine and pain killers. Take your advil separately, and for just a cold you probably don’t need cough medicine, and when you have the flu, you generally are not congested. Those medicines overmedicate people, and I already am recommending you take as much medicine as allowed that is warranted for the flight.
Most of the anthistimine/decongestant medicines on the market are every 4–6 hours. Read the directions carefully. Make sure you take just one pill if that is the recommendation, or two if that is the recommendation. The two hour point it probably when you will be most medicated so if you can time that with landing that would be ideal. By 4 hours the drugs will be leaving your system, so have the meds in your purse, including the afrin if you are delayed.
Vitamin C and zinc is not worth crap on an airplane. If you believe it helps you get over a cold faster, I am not going to argue that on this Q, but certainly you must be practical about your health and comfort for at least the few hours you are on the flight.