Face it, you're going to have to be miserable for a while, for the sake of your son and just reenforce that homework needs to be done before the fun. My experience has been if you let them off the hook and back off, they'll never learn to discipline themselves or develop a work ethic. Sure, 1st grade work is easy for him. He's lucky. But it is certainly no reason to back off on the workload or a reason to give in to his push back.
With that said, for your son, the ease can be a plus, right now. He can (you can) use this opportunity/time to focus on helping him build and develop good study habits. This is so important, because the work load and level of difficulty won't always be easy. The further along he goes in school, that work load and the expectations are inevitably going to increase. Those kids who master discipling themselves at an early age to knuckle-down, fare much better than their counterparts who shirk responsibilities saying they're bored or burned out.
His behavior should be alarming instead of exasperating. If he's doing this now, and you're ready to back down or let it slide while the workload is easy and the material simple, what will you both do when things kick into high gear in the next months or year to come?
If after the first grade ends, and he still finds things are too easy, that's when you start looking at ways to make lessons more challenging. Perhaps explore a gifted program, or homeschooling. But to me, it sounds like this is more of an attitude problem and power struggle, than an issue of the program fitting the child.
For now, I'd be sticking to my guns and make him tow the line. If you let him intimidate you over doing jobs that are an expectation, you're going to have real problems with school work and probably other issues later.
This isn't about him being all boy. All kids do this at some point. This is about teaching him responsibility and good habits, like brushing teeth, getting cleaned up every day, and doing chores around the house. You need to explain to him the importance of taking school work seriously, no matter how easy or boring because everything he does from here until graduation counts.
What does he want to do when he grows up? One of my sons wanted to be a police officer. I took him to the local police department when he was in the 2nd grade, and he was able to spend an afternoon with a few of the officers. They were fantastic! They explained how the work he's doing in school now applies to their adult jobs everyday.
My son hated writing papers and reports. They told him writing was very important since they had to write reports for every call, and those reports became important documents when and if cases had to go to prosecution. Everything they wrote mattered. My son's attitude about writing changed immediately.
The investigators showed him how important science and math was in the field and with crime scenes. He saw how they had to still go to "school" and had daily responsibilities and had to listen to their superiors and so on.
Once my son learned how things that seem silly right now really do matter, his attitude about school really changed.
Don't use toys and trinkets as a reason to get school work done. School is preparation for tommorrow. He needs to know and understand that. If he has purpose, he may be more invested in his work. Help him to set real goals and see if this approach is more effective. Kids know toys get broken...and most assume someone is going to get them what they want anyway. Maybe a mom and son career day is in order. Maybe explore and reasearch careers he's interested in and find out how his schooling now will get him to that goal. Does he know about college and which one he might want to go to? If not, take him to a local university football game and tell him how these kids were all into their homework...and will someday be doctors, lawyers, or even a professional ball player. But they wouldn't even be able to consider it if they didn't do their homework everyday because they wouldn't have had the skills to get into the school. You get the idea. Be creative.
He needs to know that school is the key to being able to be and do what he wants with his life in the future. Give him concrete examples...talk about college now...show him how short the time in school really is. Now days if he's not reading and writing at college level and most important isn't able to handle the work load when he's in middle school (which is now 6th grade - 8th grade---only 5 years from now), he probably will not be able to get into the school of his choice, let alone be able to pass the college entrance exams.
Good luck!
You need to just stand firm.