Every child is different for when they start talking. If you want your children to speak earlier then you bombard them with language from the moment they are placed in your arms, talk to them constantly about everything about nothing at all- the more they hear it the more they want to try it. I also did baby sign and they can start communicating with you even sooner.
My friend has a little boy whose language skills were about the level you are describing and he was almost three- she found out that he had serious ear infections and tonsil problems that were preventing him from hearing which was preventing him from talking. If you are concerned about it then I would have his doctor take a serious look at his ears and throat.
Your pediatrician will also have development expectation on language, whether or not your child should be putting words together for sentances and small phrases...
At 2 1/2 I would expect him to speak a little more but it may be that he prefers nonverbal communication- if he knows mom and dad will respond to his nonverbal communication he may just stick with what works- you could start having him say things before you give them to him- have him parrot you- if you know he wants milk have him repeat after you milk please before you hand it to him... Good luck