As long as you're on Ritalin, your appetite will be suppressed; however, in the evening when the effects have worn off or just before the stimulant takes effect in the mornings, you may become hungry, so eat a hearty meal. Watch your weight carefully to make sure you don't lose too much too quickly, and take a good multi-vitamin.

With respect to the alcohol, I wouldn't recommend mixing the 2, especially since you're not yet sure how the medication will affect your performance (e.g., driving, concentration), and we already know how alcohol does. On a more serious note, however, if you have problems with alcohol (abuse or dependence), the issue may not be the mixing of the 2, but the fact that stimulants are rarely prescribed to someone who has trouble managing their alcohol (and I'm not suggesting you do) since Ritalin can be easily abused, which over the long term, can only complicate your life.

You can either quit the alcohol (my suggestion at this point), or ask your MD about non-stimulant meds such as Strattera, or see a someone who specializes in applied behavior analysis to work with you on attentional difficulties. Should you decide to quit, SMART Recovery is one of the best options available as it is one of the more evidence based approaches for addictions. If you continue to drink, then make sure you do so only after you fully understand how the meds will affect you, and it's best to drink (poor phrasing I know) when the meds are mostly out of your system.

Good luck and I hope this helps,
Baaku