We will first determine whether a beracha rishona can cover that which one subsequently drinks or eats at various times and places, and then we will see what options are advisable.
Moving from house to house can sometimes require one to make a new beracha.[2] However, the problem is less acute when one starts eating outside with the intention to continue as he goes. In such a case, the change of location is not a change in mindset, and the original beracha even covers food eaten in a place that is not visible from the site of the beracha.[3] (See Igrot Moshe[4] regarding one who starts eating in the house with the intention to leave immediately.)
Therefore, in this case, it is possible to make a single beracha that will last throughout the hike, and this is indeed preferable for one who takes sips frequently and regularly. (Regarding the beracha acharona, note that, in general, one should make a beracha acharona only if he drinks a revi’it [approximately 90 ml. or 3 fl. oz.] at one time. If one merely sips, it is best to drink a revi’it at some point so that he can make the beracha acharona.[5]) However, if one takes significant breaks between drinks, the question is two-fold:

1. Can a single beracha rishona remain in effect despite all the breaks?
2. Can the eventual beracha acharona relate to that which was drunk long before?

We will start with the second question.
After partaking in a full meal, one may recite Birkat HaMazon until the last food eaten has been digested to the point that he begins to become hungry again. This takes a minimum of seventy-two minutes.[6] However, when one eats lightly or drinks, we need to consider the possibility that the food’s filling (or the drink’s quenching) effect begins to wear off more quickly. Although there is no consensus among poskim as to the maximum one can wait before making the appropriate beracha acharona, a reasonable middle-of-the-road opinion is approximately half an hour.[7] Therefore, if there are likely to be breaks of over thirty minutes, one should certainly make a beracha acharona before losing the opportunity to do so. He will subsequently be required to make a beracha rishona before resuming drinking.[8] It is still advisable to have in mind, when making the beracha rishona, that it should apply only to that which he drinks until the beracha acharona.[9] This is in deference to the opinion that if one intends to eat or drink intermittently, the beracha rishona covers even the food he eats after the beracha acharona.
Thus, if one expects to take a sip every few minutes, he should make one beracha rishona at the beginning and one beracha acharona at the end. If he plans to take long breaks, he should make both berachot each time. The better question is if one plans to drink every several minutes, but it is possible that a significant amount of time will pass. The Minchat Yitzchak’s[10] approach, addressing those who sit and learn over periodic cups of coffee, is that it is better not to rely on the prospect that he will remember to drink within the requisite time.[11] This is even more applicable on a hike, where one could become preoccupied or become thirsty very quickly, after which it is too late to make the beracha acharona.
If one took the approach to make only one set of berachot and he ends up waiting too long to make the beracha acharona, there is a major machloket what to do. The Magen Avraham[12] says that the previous eating is finished, and there is now a need for a new beracha rishona. The Even HaOzer[13] says that as long as one had in mind to continue eating or drinking, the beracha rishona is not lost. It is not clear how to rule,[14] which is one more reason to avoid the situation. There are a few ideas how to extricate oneself from doubt in such a case, but they are beyond our present scope.