For most 'serious' events, I prefer one re-buy per player, with the re-buy cost the same as the initial buy-in (or whatever was contributed to the prize pool from the initial buy-in), and available only for a limited period (generally when the current blind level dictates that the value of the re-buy is not less than 20bb).
I've experimented a lot with re-buy structure variations, and unlimited re-buys with no time restriction for very low-cost events can be a lot of fun, too.
One re-buy variant I've tried has generated interesting results -- the re-buy cost varies based on the number of big blinds at time of purchase. So if an initial buy-in of $60 received a stack of 20K chips (200BB with 50/100 opening blinds), then the cost per BB is 30c each. The price of all subsequent re-buys are then priced at that same amount (30c per BB)-- so a 20K re-buy stack at L3 (with 100/200 blinds) would be 100BB, and cost $30, and a 20K re-buy stack at L5 (200/400 blinds) would be 50BB and cost $15. The declining price of re-buys (due to the declining value of the chips) definitely promotes more aggressive - and perhaps looser - play, since the cost to re-buy is much less expensive than with more mainstream models. For this reason, I recommend stopping re-buys at between 50BB-100BB when using this re-buy model. You can also develop a sliding scale for increasing cost of BB in re-buy stacks, so that the price still drops, but not as severely as the increasing blinds devalue the stack. This actually works pretty well, and provides both good value for re-buys without players going overboard with aggression because of a steeply-discounted re-buy cost.
Less successful was experimenting with a standard price/BB for re-buys but with a fluctuating re-buy stack size -- in the example above, players re-buy a 200BB stack at the initial cost per BB, so at L3, a $60 re-buy would get a T40K stack (200BB at 100/200). It was interesting, but made re-buys way too powerful, and put way too many chips on the table. Not recommended.
I've handled bounty chips three different ways -- included with the re-buy stack, optional with the re-buy stack (but you can't win bounties without owning one), and a single bounty chip with initial buy-in only (lost only when eliminated). There's not much of a difference between the three imo, mostly just a personal preference -- aggressive players like more bounty chips (since they tend to collect more of them on average), and tight/passive players tend to dislike bounty chips at all (mostly because they rarely collect very many).
I've also offered a second-tier bounty (sometimes called a super-bounty), which is typically twice the cost of the 'standard' bounty and is an optional purchase for players who want more $$ action. Only players with a super-bounty can collect one, and if a super-bounty player is knocked out by a non-super-bounty player, they retain their own super-bounty and redeem it for cash.