What are the things which, if the person who is performing tawaaf does them, do not spoil his tawaaf?
Question

                What are the things that do not spoil tawaaf and do not make it essential to start it all over again?
Praise be to Allah.Firstly: 
One of the conditions of tawaaf being valid is doing the circuits consecutively, in the sense that the seven circuits are done one after another, without any lengthy interruption between them. 
See: al-Mughni (5/248) 
If a person does two circuits, then interrupts his tawaaf for an hour, for example, in order to go and look for his friend or to sit and chat with him, his tawaaf is rendered invalid and he must start all over again. But if the interruption is brief, such as if it is for a minute or so, then that does not spoil tawaaf. 
The scholars granted a concession to the person performing tawaaf if a bier is brought for the funeral prayer, or the iqaamah (call immediately preceding an obligatory prayer) is given; in that case he may pray and then complete his tawaaf, and does not have to start all over again. 
It says in al-Mawsoo‘ah al-Fiqhiyyah (8/213): 
The fuqaha’ are unanimously agreed that if a person begins tawaaf, then the iqaamah is given for an obligatory prayer, he may interrupt his tawaaf and pray with the congregation, then he may resume his tawaaf, because he did something that is prescribed, so it did not spoil his tawaaf, like a brief action. 
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said: 
Continuity between the circuits of tawaaf is an essential condition, but some of the scholars granted a concession for things such as the funeral prayer, or becoming tired and resting for a moment, then resuming tawaaf, and so on. 
End quote from Majmoo‘ Fataawa wa Rasaa’il al-‘Uthaymeen (22/296) 
He also said: 
With regard to tawaaf and sa‘i, it is stipulated that it be done continually, which means making the circuits consecutive. If there is a lengthy interruption between them, the first circuits are rendered invalid, and the individual must start tawaaf all over again. But if the interruption is brief, such as if he sits down for two or three minutes, then gets up and completes his tawaaf, there is nothing wrong with that. But if the interruption lasts for an hour or two, then this is a lengthy interruption which means that he must repeat tawaaf.
End quote from al-Liqa’ ash-Shahri (16/22) 
The shaykh (may Allah have mercy on him) was asked: 
If a person does four circuits of tawaaf, then he interrupts tawaaf because of prayer or the crowds, then completes it after that, after an interruption of twenty-five minutes, what is the ruling on this tawaaf? 
He replied: 
This tawaaf was interrupted by a lengthy interruption; if he had interrupted it for the prayer, that would have been a brief interruption, because the prayer does not take longer than ten minutes, or quarter of an hour, or thereabouts. But twenty-five minutes is a lengthy interruption which makes it invalid to connect the circuits to one another. Based on that, he must repeat his tawaaf in order for it to be valid, because tawaaf is a single act of worship, so it is not possible to do its parts piecemeal, with interruptions of twenty-five minutes or more between its parts. 
End quote from Majmoo‘ Fataawa wa Rasaa’il al-‘Uthaymeen (22/296) 
Shaykh Ibn Jibreen (may Allah have mercy on him) was asked: 
We did tawaaf al-ifaadah, and when we began tawaaf, in the first circuit we completed it, but the crowds were too much, so we went up to the second floor (of the mosque) to complete our tawaaf there. But we were still not able to complete it because the crowds were too much, so we went up onto the roof and we completed the remaining circuits on the roof. Is the tawaaf we did in this manner valid, or do we have to repeat it? 
He replied: 
It is valid, and you are excused, although it would have been better for you to be patient and put up with the crowds in the courtyard. But because you found it too difficult and you went up to the second floor and did one or two more circuits there, but you were not able to complete it, so you went up to the roof, all of that is excused. 
End quote from the shaykh’s website:
http://ibn-jebreen.com/books/8-224-7689-3317.htm
Secondly: 
One of the conditions of tawaaf being valid, according to the majority of scholars, is being free of minor impurity. So if the person who is performing tawaaf loses his wudoo’, his tawaaf is rendered invalid – according to this view – and he has to do wudoo’ and repeat his tawaaf. However there is a difference of scholarly opinion concerning this matter, which has been discussed in fatwa no. 34695 
Thirdly: 
Tawaaf is not spoiled by eating, drinking, sleeping or speaking. 
An-Nawawi (may Allah have mercy on him) said: 
It is makrooh (disliked) for the person performing tawaaf to eat whilst doing it, and the objection to his drinking is less emphatic, but tawaaf is not rendered invalid by either or both of these actions. 
Ash-Shaafa‘i said:
There is nothing wrong with drinking water whilst doing tawaaf and it is not makrooh – in the sense of it being a sin – but I prefer not doing that, because not doing it is better in terms of etiquette. 
End quote from al-Majmoo‘ (6/46) 
He also said: 
If a person falls asleep whilst doing tawaaf or partway through it, in a way that does not invalidate his wudoo’, then the more correct view is that his tawaaf is still valid in that case.
End quote from al-Majmoo‘ (8/16) 
Al-Khateeb ash-Sharbeeni (may Allah have mercy on him) said: 
If he falls asleep whilst doing tawaaf in a manner that does not invalidate his wudoo’, his tawaaf is not spoiled. 
End quote from Mughni al-Muhtaaj (2/244)
Limiting sleep to that which does that not invalidate wudoo’ is based on what is referred to above of the difference of scholarly opinion concerning that, which is whether being free of minor impurity is essential in order for tawaaf to be valid. 
Shaykh Saalih al-Fawzaan (may Allah preserve him) said: 
Talking whilst doing tawaaf is permissible, but it is better for the Muslim who is circumambulating the House of Allah, may He be exalted, to focus on worship, dhikr and du‘aa’, and not to be distracted by ordinary talk, because being distracted by ordinary talk is contrary to what is preferable. But that does not affect the validity of his tawaaf. Permissible kinds of talk do not affect the validity of tawaaf, although not doing that is preferable. 
End quote from Majmoo‘ Fataawa ash-Shaykh Saalih ibn Fawzaan (2/485)  
And Allah knows best.