As a former preschool teacher, I'm telling you, CONSTANTLY tell him, "You can do ANYTHING you put your mind to." I don't care if you have to say that 500 times a day. I also NEVER allowed the "C" word.
If kids - and even when I coached at the collegiate level" told me they "couldn't"........I would remind them that the word was NOT allowed and make them REPEAT to me that they could do it, however, they just either needed help or just needed a break - and sometimes, especially when it comes to physical skills they DO need a break. DON'T let the "break" phrase become a cause for giving up though.
As you are driving and talking, ask about things you see along the way..."stoplight". What letter would "stoplight" begin with? Give him a letter to find.."S" like in "STOP". There are TONS of signs on businesses and finding letter shouldn't be that hard. AND.....it gives them something to DO!
Remember to tell him how smart he is when he finds them. Use stop lights/signs to start math. How many stoplights to get to the grocery store? Then, after he masters that....use it for subtraction. IT WORKS! I started doing this with Abbie when she was 3. She's now 7 and excels at spelling AND math.
In addition, you might look into the LEARNING LEAPFROG set that has letters, phonics, capitals, lower case, words, etc. It gives you sounds, shows you how to write the letter and gives you a chance to practice it. THIS IS PHENOMINAL! I think it was a HUGE factor in giving her an excellent start.
When it comes to things around the house, let him help...i.e. setting the table, putting clothes into the dryer, etc. THEN, little by little, give him SMALL tasks to do on his own, even if you are right beside him. The more you do something, the more confidence you gain. Doesn't change even as an adult!
I now have a 7 year old who thinks she's an expert at cooking and working out, besides reading, spelling and math.
Remind him how much you need his "help". This builds confidence, too. Everyone needs to be needed rather than NEED to be connected at the hip.
DO NOT ALLOW WHINING. If they whine, they DON'T get whatever it is they are whining about. I remind them that whining is not allowed or appropriate, nor will I respond to it. You learn to ASK...communicate. Talk about appropriate words, emotions, actions, etc. Give him ALTERNATIVES to the whining, etc. Unfortunately, there are adults who STILL haven't learned this!