Answer
Wa `alaykum as-salamu wa rahmatullahi wa barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
Brother, thank you for your good question and concern about halal foods and drinks.
A Muslim is allowed to eat the food prepared by the people of the Book as long as the food itself is good and halal. One therefore may eat at kosher restaurants good permissible food.
Answering your question, Dr. Wael Shehab, PhD in Islamic Studies from Al-Azhar University and currently the Imam of the Downtown Toronto Masjid in Canada, states:
Allah tells us in the Qur’an that we may eat of the good food of Christians and Jews. Therefore, unless there is a specific reason for the prohibition of a particular type of food prepared by such people, it is permissible to eat it. Allah says in the Qur’an:
“Today, I have permitted for you all good things, and the food of the People of the Book is permissible for you, and your food is permissible for them.” (Al-Ma’idah 5:5)
Therefore, you are first advised to look for halal/Islamic restaurants or stores to have food therefrom. If you don’t find, you may eat at kosher restaurants meals or foods that are free of ingredients that are considered haram.
And, don’t forget to say the basmallah (in the Name of God) before you eat. Al-Bukhari narrated on the authority of `A’ishah (may Allah be pleased with her): “Some people who had recently embraced Islam said to the Prophet (peace and blessings be upon him), ‘People bring us meat and we do not know whether they have mentioned the Name of Allah when slaughtering it or not. Shall we eat of it or not?’ The Prophet (peace and blessings be upon him) replied, ‘Mention the Name of Allah (over it) and eat.’“
Allah Almighty knows best.