I do not know of any foods or herbs that have been shown scientifically to have significant beta blocking activity. Alcohol and mood altering drugs are not related in any way to beta blockers. Any time one introduces a foreign substance into the body, one is taking a risk of an adverse effect. This applies to aspirin, tylenol, nicotene, ethanol, etc. Beta blockers are among the safest of medications, used by millions with only very rare adverse reactions.
Allergic reactions can occur to any medication, but are quite rare with beta blockers.
Extremely low blood pressure from a beta blocker is also extremely rare. One very predictable adverse reaction, however, is a worsening of asthma. Beta blockers will tend to close the airways. Someone with normal lungs will not notice any change, but an asthmatic person, with already narrowed airways, will risk a severe asthma attack. No one with any history of asthma should consider taking a beta blocker except under close direct medical supervision and for the strongest of medical indications.