His eminence, As-Sheikh ‘ATiyyah Ṣoqr-may Allah have mercy on him, says in his book: ‘Finest Speech on Rulings and Judgements’:

Generally, there is no dignity in eating food on the road – there might not be evidence that prohibit it, however, it must be done far away from people’s sight in order to prevent criticism and the indigent who are in need of it but deprived of it. It is also important to avoid a situation where something gets into the food from the soil and mixes up and it is difficult to remove/purify it or there is contamination/pollution. 

Narrated by Ahmad, Ibn Majah and Tirmidhy and it is authentic, that Ibn Umar, may Allah’s peace be on both of them said:

“At the time of the Messenger of Allah () we used to eat while walking, and drink while standing up.” 

There is no dignity in taking a drink while standing even if it is simply disliked and not forbidden. In following the way of the messenger, may Allah’s peace and blessings be upon him, where most of his drinking was done while sitting, and he discouraged drinking while standing though he did drink once while standing. That is to illustrate the permissibility of either way. Or  there is a reason/cause preventing him from sitting. Zamzam was brought and they took from it, then he picked the bucket and drank while standing. ‘