As far as I know the verb go can be used as in "go + to + infinitive" and "go + gerund". In other words, in the examples I have posted below, cases 1 and 3 are correct. Am I right? I often have doubts with these forms.
1. "In the meantime I'll go fetch my laptop computer"
2. "In the meantime I'll go to fetch my laptop computer"
3. "In the meantime I'm going to have lunch"
4. "In the meantime I'm going have lunch"
1. is good idiomatic American English -- British English prefers "and" between "go" and "fetch".
2. is grammatically possible but unusual and unnatural.
3. is an example of the "to be + going to + verb" construction used to describe an event that is about to take place, or which is definitely planned.
4. is simply ungrammatical.