Drinking liquids after Kiddush prior to the meal:
It is permitted for one who is thirsty to drink after Kiddush, prior to the meal.
Saying a blessing prior to drinking: One who drinks prior to the meal is not to say a blessing over the liquid if [he drank from the Kiddush wine and] had in mind to drink this liquid at the time of Kiddush. Likewise, even if he did not have in mind to drink the liquid at the time of Kiddush, if the liquid was on the table, it is included in the blessing of Hagafen. If one did not have any Kiddush wine, or did not have in mind to drink the liquid during Kiddush and the liquid was not on the table, then a blessing is to be recited prior to drinking. [This applies even if the drinks were brought while one was still in the middle of drinking the wine, nevertheless the blessing of Shehakol must be recited.]
Saying a blessing after the drinking: One who drank wine [or other alcoholic beverages] after Kiddush, prior to the meal, is not required to say an after blessing on these liquids. If, however, he drank other beverages he is required to say an after blessing after drinking it. This however only applies if he does not plan to drink a Revius from the Kos Shel Bracha for Birchas Hamazon. If, however, he will drink a Revius of wine from the Kos Shel Bracha after Birchas Hamazon, and hence will say an after blessing after this wine, then he is not to say an after blessing on any liquids drunk after Kiddush, prior to the meal.
 See Admur 249/10-11 and Kuntrus Achron 249/4 that the prohibition of eating between Kiddush and the meal is only if a) one is saying a blessing over the food [as then there is a question of a saying an unnecessary blessing, and of breaking the laws of precedence] and b) one can wait to eat the food during the meal and is preceding it to the meal simply for the sake of the blessing [see Admur ibid and Kuntrus Achron ibid] and c) It satiates the person. Thus, in this case that one is simply drinking and not eating, in which case there is no satiation, and he is not saying a blessing over the drink, being it is covered by the Hagafen over the wine, there is no prohibition at all involved in drinking it prior to the meal. Furthermore, even if a blessing is required to be made over the drink, if one is drinking it due to thirst and does not want to wait until later, there is no prohibition involved in saying a blessing over the drink.
 Seder 1/21; Luach 5/11; Admur 174/4 and 7; 204/12; 272/13; Michaber 174/2 and 208/16; Rabbeinu Yona Brachos 29a; Rosh Brachos 26; Rebbe Chiya in Brachos 41b; Ketzos Hashulchan 53/13 and 60/7; M”B and Kaf Hachaim on 174 and 208 ibid; Piskeiy Teshuvos 174/1-7
 Derech Hachaim Hilchos Kiddush; M”B 174/3
 Admur Seder and Luach ibid; 174/4 in parentheses; Elya Raba 174/8; Implication of M”A 174/11 and 206/6 and 272/9; Makor Chaim of Chavos Yair; Shulchan Hatahor 174/2; Chayeh Adam 55/4; 2nd opinion in M”B 174/2, in name of Admur and Mahram Benet; Kaf Hachaim 174/11; Shevet Halevi 3/16; See Piskeiy Teshuvos 174 footnote 14
Other opinions: Some Poskim rule the other liquids are not exempt unless they were on the table at the time of the blessing [or later on if is drinking Bekevius]. [1st opinion in M”B ibid] Based on this, some Poskim conclude one is to always have the drinks on the table in order to exempt it with the blessing of the wine. [M”B ibid]
 Admur Seder and Luach ibid; 174/4; M”A 208/24; Taz 174/2; Mordechai 150
 Admur Seder ibid
 Implication of Admur ibid who makes no differentiation; Taz 174/2 in name of Mordechai that today there is no Kevius by wine; Chayeh Adam 55/5; Ketzos Hashulchan ibid footnote 27 that so is implied from Admur ibid even though in 213 he rules there is Kevius by wine, although concludes with Tzaruch Iyun [See there in length for a discussion on this matter]
Other opinions: Some Poskim rule that only if one was not drinking the wine Bekvius do we mandate a new blessing to be recited. If however one is drinking wine Bekevius, and is still in the midst of drinking the wine, then if other drinks are brought, they are exempt from the blessing of Shehakol, even though one did not have them in mind at the time of the blessing. [Implication of Mordechai ibid; Darkei Moshe 174; Kneses Hagedola; Shelah; Elya Raba 174/8; Degul Merivava on 174; Shaareiy Teshuvah 174/1; P”M 174 M”Z 2; Nehar Shalom 174/2; Derech Hachaim; Magen Giborim; M”B 174/3; Kaf Hachaim 174/4]
 Admur 272/13 in parentheses; Ketzos Hashulchan 60/7 and 79/11; Piskeiy Teshuvos 174/4; Based on: Admur 174/6; Seder 4/11 and so rules M”B 174/25, that whenever one has drinks before a meal, they are not exempt with the Birchas Hamazon
Other opinions: Some Poskim rule one is never to say an after blessing on a drink prior to a meal, even if one said a blessing on Shehakol over them. [Taz, Elya Raba, Olas Tamid, brought in Biur Halacha 174/6 “Veafilu”; See Piskeiy Teshuvos 174/4]
 Admur 174/6
 The reason: As they included in the foods eaten as part of the meal, and hence exempt with Birchas Hamazon.