Drinking while wearing Tefillin?

Question

Is one allowed to drink (coffee) while wearing Tefillin? Or for that matter, any other drink.

Answer 1

The answer is directly drawn from Gemara.

Gemara Berachot 23b:

אמר רבי יצחק: הנכנס לסעודת קבע - חולץ תפיליו ואחר כך נכנס.‏

R`Isaac said: One who wishes to [partake of] a regular meal should take off his tefillin and then go in {since it may become drunk and will demean himself with Tefilin. Rashi}.

ופליגא דרבי חייא, דאמר רבי חייא: מניחן על שלחנו, וכן הדור לו. ועד אימת? אמר רב נחמן בר יצחק: עד זמן ברכה. ‏

He differs from Rabbi Hiyya; for Rabbi Hiyya said: He places them on his table {so he can go into the meal room with Tefilin and putting them on table}, and so it is becoming for him {to be available to take them for time of blessing (graces) }. How long does he leave them there? Until the time for grace.

See Rambam Sefer Ahava hilchot Tefilin, chapter 4, halacha 16 follows the opinion of Rabbi Chyia:

וְאֵינוּ אוֹכֵל בָּהֶן, אֵלָא אֲכִילַת עֲרַאי; אֲבָל אִם נִכְנַס לִסְעוֹדַת קְבָע--חוֹלְצָן וּמַנִּיחָן עַל שֻׁלְחָנוֹ עַד שֶׁיִּטֹּל יָדָיו, וְאַחַר כָּךְ יַנִּיחֵם, וִיבָרַךְ עַל מְזוֹנוֹ, וְהוּא לָבוּשׁ בָּהֶן.‏

He may eat only a snack while wearing them. If, however, he enters to partake of a regular meal, he should remove them and place them on the table until after he washes his hands [at the conclusion of the meal]. Afterwards, he should put them on and recite grace over his meal while wearing them.

Shulchan Aruch said the same:

ח הַנִּכְנָס לִסְעֻדַּת קֶבַע, חוֹלְצָן וּמְנִיחָן עַל הַשֻּׁלְחָן, עַד זְמַן בְּרָכָה, וְחוֹזֵר וּמְנִיחָן. אֲבָל לַאֲכִילַת עֲרַאי אֵין צָרִיךְ לְחָלְצָן: ‏

Conclusion: That is perfectly allowed to drink a Coffee wearing tefilin.

Answer 2

Seudat Keva is forbidden, but Arai is allowed. Coffee is usually drunk as a Keva meal, a permanent meal, so in that case i think it would be forbidden, but then again if it is a part of some kiddush after Tefillah, and one is still wearing his Tefillin, in my opinion it's considered Arai, and is allowed. והשם יראה ללבב.

Consequently, light drinks, such as water or soda, are allowed anyways.

Plus, fruit and vegetables are allowed too.

Sources: Shulchan Aruch (OC 40:8), http://www.chabad.org.il/Magazines/Article.asp?ArticleID=3440&CategoryID=908