Some activities which come to mind include playing some sport, drawing or even playing video games.
Though, I would be extra careful with video games nowadays, since many of them include mechanics which are very similar to gambling and encourage the player to spend real money in order to partake on them.
Playing video games is not always effective in overcoming gambling addiction depending on individual personality, some adventurous or war video games might help fill the time to avoid gambling activities without buying any items from the game.
For me the main solution to disappearing gambling is that he has committed not to gamble anymore and avoids the gambling environment or keeps his distance from his gambling friends, he has to find a new environment to forget his past and has to have more activities outside to hang out with friends. He must change his mindset to appreciate the income from hard work not to be wasted on gambling, but apply his financial management to family needs and financial needs for your future.
Dodging gambling instead of learning how to control your gambling problem will just give you problem in the future in case you successfully manage to avoid gambling today since you still have a risk to become addicted again once you become exposed again in the future.
Gambling is not a drugs which is illegal and can harm when you use. You will need to face it if you are already exposed to it and solve your addiction by slowly reducing your gambling activities up to the point which you are not craving anymore for more instead of completely removing it out of your system by just avoiding it. We always have urge on things that like.