I -- This is from the first-person form of the verb.

have compassion -- The Greek term that KJV translates as "I have compassion" is only used in the New Testament and only three times in Jesus's words. It doesn't exist elsewhere in Greek literature.  It is based on the general Greek term for the inner organs. It is connected to the idea that the inner organs are the seat of human feelings (something supported by recent research into brain). The English terms "eating one's heart out" and having "gut feelings" or having one's "insides ache" carry a similar sensibility. There is also a religious side that has no parallel in English because the term is also linguistically related to the idea of eating the inner organs of an altar sacrifice.

for -- The word translated as "on" means "against", "before", "during", "by" or "on." The word translated as "on" means "against", "before", "during", "by" or "on." With the objective noun, as used here, it means of place: "upon or on to a height," "up to," "as far as," "a little way," "a little," "towards," "to," in hostile sense: "against," of extension: "over," "over (a space)," of time: "for," "during," "up to" or "till," in a causal sense: "of (the object)," for (this purpose)," "as regards," "according to," and "by (this cause)."

these -- The word translated as "the" is the Greek definite article. The Greek article is much closer to our demonstrative pronouns ("this", "that", "these", "those"). See this article for more. 

people,  -- (WW) The Greek word translated as "the multitude" means "a throng" or "multitude" but which also mean "trouble" and "annoyance." Our word "mob" or "crowd" really captures the idea best.

missing "because"  -- (MW) The untranslated word  The word translated as "because" introduces a statement of fact or cause.

they  -- This is from the third person plural form of the verb.

have -- (WT) This helping verb "have" indicates that the verb is the tense indicating an action completed in the past. This is not the tense of the verb here.

already -- "Already " is an adverb that means "already", "by this time", "forthwith", "after", "immediately," and "now." It means proximity in time, but also place.

been -  (CW) "Been" is a verb that means "to wait" with a direct object, but "to remain attached," and "to cleave to" with an indirect object.  The verb is plural. 

with -- The form of the following noun requires that addition of a preposition in English to capture its meaning, a "to" as an indirect object, a "with" for instruments, an "in" for locations, an "as" for purposes, an "of" for possession, a "by" for agents, an "as" for comparisons, and an "in" for area of effect.

me -- The "me" is in the indirect object form on the first-person pronoun, so usually "to me", though the form has other uses in Greek. 

three -- This is the Greek word for the number three.

days, -- The Greek word translated as "day" also means "time," in general, and refers specifically to the "daytime."  The form of the word is a subject so the sense is "it is" three days". 

and -- The Greek word translated as "and" is used as the conjunction "and", but it also is used to add emphasis ("also"). In a series, it is best translated as "not only...but also." After words implying sameness "as".

have -- The word translated as "have" means "to possess" or "to keep" but it isn't used in the same way as a "helper" verb that the English "have" is.

nothing -- (CW) This is from two Greek word meaning "not anything." The Greek word "not" is the Greek negative used to deny objective facts, not opinions nut it doesn't modify "anything" but the verb "have." It makes a negative statement of fact. When a negative precedes the verb, it affects the whole clause. When it precedes other words, its force is limited to those words.  The Greek word "anything" in the singular means "anyone", "someone," and "anything." This is not the common word meaning "nothing."

to --  (WF) This "to" is added because the infinitive form of the verb requires a "to" in English. This verb is not an infinitve, but an active verb.

eat: -- The word translated as "to eat" is one of the two common words used to mean "eat."It means "to eat", "to eat up," and "to devour." The form is third-person, plural, subjunctive. Its sense is "they should eat."