Coffee! Yes! Do not stop cold! Taper off over about three days or risk the dreaded caffeine headache! I drink only one weenie cup of instant a day and it will still kick my hiney.
If you are starting the cleanse and have not tapered off, as I have done a couple times in the past, Have 1/2 cup the first day, a bit less the second... THEN stop. I have done this while starting the Master-Cleanse and done fine, avoided the headache.
As far as what to expect, those first three days are traditionally the worst, although you can really minimize discomfort if you do a precleanse diet of fruits and vegetables, lots of water, and taper off your caffeine during that period.
If you have not done a precleanse diet, you are still ok if you eat a healthy diet. If you are pretty toxic, you may well feel pretty funky for a few days. Drink lots of water in addition to your lemonade, keep your colon moving along and if you don't feel great, baby yourself a little.
By the fourth day you should be sailing along, again depending on how toxic you are. I have been cleansing for eight years (!) now (I can't believe it), having attained my main goal of a clean pink colon midway through the eight years. Since I cleaned up my act fasting is a real pleasure. Prior to that... I had my moments for sure.
Whatever your cleansing goals, I am a poster child: You can do it!
And if you're serious about cleansing, don't forget to have a look at the wonderfully informative and supportive Liver Flush Forum . Liver Flushing absolutely changed my health for the better. If you have a clean colon and a clean liver, life is good!!