If you've been friends with them for a while then that shouldn't be too hard, I suppose.
Simply, don't change.
Surely, your friend thought he'd like to help his friends and that includes you. That should make you happy for having someone who cares for you.
However, you, as his friend, should explain to him that, before going crazy about helping people who could suck his life and money and drop him when he's no good anymore, he should look into ways to preserve his new wealth.
Also, remind him that many people have won and lost. After such events, they were left feeling miserable, worse than prior to their sudden success.
Advise him/her to seek expert advice from multiple independent parties and study the best way to make good use of his money.
And when he offers you something, it will be your decision whether you accept it or not but I suppose accepting a beer or one celebratory dinner will be fine but a house, a car or even a laptop seems very disproportionate.
Even if you weren't able to reciprocate a dinner, you can always give him your friendship. Look after his interests instead of your own. Show him insights about who's looking for his money (assuming you actually know), introduce him to your sister (if she's not a gold digger! Surely not but just saying), let him be himself, keep him honest with himself when he's going all crazy with his money in parties, etc.
How do I see this advice being used and working?
In my life. I have 2 friends whom I am going to call Charles and John.
Charles has always been the rich kid, extremely popular but friend to his friends. Some of his friends have taken advantage of him as he grew up. I met him when he was 17 and his closest friend never paid for anything because he was less fortunate which, to some extent was very true. Not poor but money couldn't be spent so frivolously.
Several times, at different points in our lives, Charles confessed to me that he felt used by his best friend. At some point, offers aside he was owed 1,000€ (we're talking young adults going to university - probably 20 years old at the time).
Charles never liked confrontation so talking about it was out of the question. Very recently, Charles confessed again that he was still upset with the situation as he never got recognition for helping out his friend. He never wanted his money-back, just to feel appreciated.
My other friend, John, refers to other people looking after his money as gold-diggers. However, he has no problems talking to me about how much he makes after I ask explicitly. Something he wouldn't do with just any person. Well, he knows that I'm not looking after his money because I always looked after his interests, not mine.
"Looking after his interests" means giving insights about things I looked up about money, for example. This happens with some frequency, actually. Other personal matters too but that's outside the scope.
Plus, if I have the chance to offer him something like a dinner, I do. Once I sent him a portwine vintage dated from his birthyear and he loved it.
So, I suggest that if you conduct yourself with dignity and always acting your friend's best interests, you'll be fine.
As years pass by, if they deserve you as a friend, they'll recognise for who you are.