Lots of people get pregnant while coffee or alcohol drinkers. But it is better to not be putting things like caffeine and alcohol (and nicotine and MSG and nitrates and....) into your system in general and especially TTC and during pregnancy and breastfeeding IMO. Lots of docs say anything in moderation and that is great to hear but harder to believe. I don't think it would keep you from getting pregnant but it is not good for you anyway - and during pregnancy, you would want to stop anyway (I assume) so why not go ahead now? I quit drinking pop and coffee while in college - in preparation for TTC someday. I don't drink alcohol anyway. Never have smoked. Conceived first month trying with dd1 and dd2. Took five months with #3 but I contribute that to aging eggs.
There are so many things "they" (doctors, general public, whomever) believe at one point to be safe or have no affect on us but are later found to be related to problems. You may even have other positive outcomes from dropping caffeine and alcohol. A friend of mine quit having migraines after she stopped drinking diet pop. You just never know what negative effect a food/drink or drug is having.
Good luck ttc! It is a trying and exciting time. Hope you have a positive report this month!