This is basic general things you can do in whatever game you are playing to increase play time and maybe enhance the experience by doing more in the game.
-Replay the game-
If you haven't played the game in awhile then this may be a great opportunity to replay it all over again, start a new file and start playing the adventure all over again, feel the nostalgia of playing the game that you first played long ago.
Complete the game as well as complete and collect everything up to 100% completion, this also includes everything that isn't listed for 100% completion that can still be completed and unlocked that don't add to the 100% total, also unlock and collect every little thing that can be unlocked and collected, also collect all the small purposeless things as well in the game including trophies and awards if you want.
-Max Stats and Everything-
Alternatively max out everything from money, coins, items, lives, points, and whatever else there is to max out, you can do it at your own pace or come back to it later in time anyway, some games simply don't have a maximum for some stats or it may take a long time and alot of effort to max out everything, do it as you feel and see fit, it can get boring though and you don't have to do it all at once or even at all.
-Play Alternate Game Modes-
In addition to the main game, sometimes there's modes for multiplayer or battle modes or fun mini-games or alternate play modes, don't hog the game for yourself if you have multiplayer, or only play once for the quick thrill if there's so much more, have a big fun game, try all the other modes, have a 4 player battle game, challenge each mode and even play on other difficulties.
-Make up your own Adventure-
Make up your own little quest or adventure, you have to go to some place to see some character or visit somewhere, or even try to get up to somewhere that you're not suppose to, like a glitch hunter, maybe you want to use some item or something to try to do something different, perhaps you want to accomplish something in a fairly specific way or with something specific, maybe you even heard or were told some rumor about the game that you must explore, anyway it's your adventure, simply enjoy it.
-Make up your own Challenge-
Simply come up with a new challenge that you want to test out, see if it's worth doing and that it's unique compared to other existing challenges, who knows, it might get listed on some official resource.