You must keep records of everything that affects your capital gains and capital losses. Penalties can apply if you do not keep the records for at least five years after the relevant CGT event.
Keeping adequate records of all expenditure will help you correctly work out the amount of capital gain or capital loss you have made when a CGT event happens. It will also help to make sure you do not pay more CGT than is necessary. If you have applied a net capital loss, you should generally keep your records of the CGT event that resulted in the loss for four years from the income year when the net capital loss is fully applied.
Keeping good records can help your beneficiaries reduce the impact of CGT after you die. If you leave an asset to another person, the asset may be subject to CGT when a CGT event happens to that asset in the future - for example, if your daughter (the beneficiary) sells the shares (the asset) you have left her in your will.