$OctopusPackage = get-item $OctopusParameters['Octopus.Tentacle.CurrentDeployment.PackageFilePath']

#Octopus adds a GUID to the package name when it drops them on disk (i.e MyPackage.20160309.10.nupkg-e9ba4f11-9303-485f-8abc-6ea6c3776588), so you need to get your hands a bit dirty to clean it up:

#Dir where the package with the clean name will be dropped
$CopyDir = "C:\TempPackages"
If(!(Test-Path $CopyDir)){
    New-Item $CopyDir -ItemType Directory -verbose
}


#building string of full path of the package you'll be uploading
$PackageToUploadPath = (Join-Path -path $CopyDir -childpath (($OctopusPackage.Name -split "nupkg")[0] + "nupkg"))

#Creating the copy with the right name
Copy-Item -Path $OctopusPAckage.FullName -Destination $PackageToUploadPath -Verbose -Force

#Here do your magic to push the package to azure using $PackageToUploadPath

#Finally delete the copy on disk with the clean name to avoid taking too much space
#Remove-Item $PackageToUploadPath -Verbose