Donald Trump's family will be the main attraction at a fundraiser the day after the inauguration, celebrating hunters, shooters and fishermen who probably pushed Trump over the line in November.

TMZ obtained a draft of the invite for "Opening Day," a massive party that will be thrown at the Walter E. Washington Convention Center in D.C.

The attire is "Camouflage & Cufflinks ... Jeans, boots and hats are welcome."

Now, here's what you get ... for a price.

-- BALD EAGLE PACKAGE ... a private reception for 16 guests to rub elbows with Donald J. Trump. The package includes a "multi-day hunting and/or fishing excursion for 4 guests with Donald Trump Jr. and/or Eric Trump." You also get 85 VIP guest tickets to the event. Price: $1 MILLION.

-- GRIZZLY BEAR PACKAGE ... private reception for 8 people to meet and greet Donald J. Trump. The hunting/fishing trip is also part of the package. It's a scaled-down version of the Bald Eagle Package. Price: $500,000.

There are other packages as well. As for the entertainment, Alabama and Toby Keith will perform.

Our sources say it's still not clear if President Trump will attend ... they're all working on the details, and if he's not there it could affect price. That said, the event is legit and the Trump family is behind it.

Our sources say "Opening Day" is being thrown to thank the hunting, shooting and fishing communities for their support. It's something mainstream media didn't cover, but Donald Trump Jr. and others spent a lot of time in Michigan, Ohio, Pennsylvania and Iowa ... all states with a huge population of hunters, fishermen and gun enthusiasts.

Our Trump sources believe these people came out in force and made the difference in the election.