Question
How to make sure that a player that rolled awful stats will still have an awesome time at the table? What possibilities are available for the DM? Would it feel cheap to find stat-boosting items? What can players do to make sure that player is still having fun?
The simple solution of re-rolling the stats is out of the question. The adventure has already begun and it would feel very unsatisfying if the original rolling carried no weight at all.
Background
Starting a new adventure, we all decided to roll stats (highest 3 of 4d6) for our new characters. Most people rolled stats close to what one would get with point-buy, but one player had all stats in the range 8 to 11 and averaged below 10 (which is worse than a commoner).
The players are all quite new to the game and it is the debut for the GM. We all had some laughs on the horrible rolls and everyone is still having fun. The player has not complained yet, but my worry is that it will feel less fun in the long run.
The player picked druid, so they can wild-shape away the physical stats at level 2.
Best Answer
You won't like some of these answers...
Ask your table and your player what they want
Ask the table openly. "Bob just rolled really bad stats, and I don't want to hold him up to that. Would you guys think it's fair if we let him re-roll?"
Ask the player directly. "I'm going to find it really hard to tailor encounters for you, because your ability scores are so low. Do you think you'll have fun? What would you want to do if you could fix it?"
And then, most importantly, listen to their answers. They'll probably tell you exactly what you should do.
Tailor encounters such that ability scores are not important
Puzzles, social interactions that do not involve rolling, things that can be solved by spells that do not have saving throws, attack rolls, or ability checks -- such as Detect Thoughts, Minor Illusion, Comprehend Languages, etc -- will go a long way to giving utility to a commoner-type character. If you place the burden of the encounters on the players, not the characters, then you are giving everyone, including the low-stats character, an equal chance.
Of course, this cannot be done in every encounter. Sometimes, combat will happen. And that character may not have too much utility then.
Allow them to change classes into a pure support type
Give them magic items
Re-roll their stats or have them use point buy
If you are the DM, then it is within your rights to implement this solution. Put a narrative spin to it like their inner spirit has awakened due to intense trauma/stress.
If you are not the DM, and you are not being allowed to roll, express your concerns to the DM that this is not fun for you. Most DMs will listen to their players if they express their concerns.
Kill them off
An extreme solution, I'll admit, but if you as the DM don't want to re-roll stats, then kill this commoner adventurer who's tagging along with the party. People like that are simply not cut out to be an adventurer, and death is a part of the risk of adventuring. Now that he's dead, you can have them roll up new stats for a new character.
If you are the player, I'd hate to say kill your character... but kill your character. If you are truly unhappy with it, then you cannot and should not try to address the problem by tacking on band-aid solutions to it. It's not worth the stress and tension to keep dedicating your time to playing something you're not enjoying.