The Saddlers, who were playing Villa in their first official pre-season friendly today, have had several free agents training with them in an effort to win deals.
Ex-Fulham striker Timmy Abraham has been among those on trial, and Flynn has been impressed with a 'couple of wildcards'.
"We have let a couple of trialists go, but in the main, the standard of trialists I've had this season is the best I've had as a manager," said Flynn.
"We've tried to pick the right ones. There's been a couple of wildcards who have really surprised me.
"There's one or two which would be for the future, and a couple who have come in and really put their hands up to try to win a contract.
"There's players I know, and I know what they can do once they're fully fit.
"Trust me, they would be good additions to the squad, but we've got to make it work.
"There's players still to go out because I've got to be conscious of the budget. We can't just go and sign, sign, sign."
Walsall have had trialists feature in training matches against both Barnsley and Birmingham City.
When asked if any could feature against Villa, Flynn added: "Possibly. We've focused on fitness for the first couple of weeks of pre-season, setting out the demands, expectations and rules.
"We've got that into them and that's what has made them gel quicker.
"Over the next three weeks, we'll be working extremely hard on shape, movement, roles and responsibilities, throw-ins – which are a big bug-bear of mine as it's a simple thing done so bad by so many. We'll be working hard on all that."