download package dependancies and get them ready to deploy offline

convoy.sh

#!/bin/bash
# Convoy downloads the stuff you need per package name for debian/ubuntu
# Requirements: dpkg-dev
# Example: ./convoy.sh python3-pip
get list of dependancies and download
sudo apt-get download $(apt-cache depends --recurse --no-recommends --no-suggests --no-conflicts --no-breaks --no-replaces --no-enhances "$1" | grep "^\w" | sort -u)
# create necessary Packages.gz file
sudo dpkg-scanpackages . | gzip -9c > Packages.gz
# gzipped all of it and ready
tar czvf convoyed.tar.gz .

On target machine run the following:
# echo "deb [trusted=yes] file:<your folder here> ./ | sudo tee -a /etc/apt/sources.list

Updated:

#!/bin/bash

# Convoy downloads the dependencies for a specified package name for Debian/Ubuntu
# Requirements: dpkg-dev
# Example: ./convoy.sh python3-pip

if [ -z "$1" ]; then
  read -p "Enter the package name: " package_name
else
  package_name="$1"
fi

# Get list of dependencies and download
sudo apt-get download $(apt-cache depends --recurse --no-recommends --no-suggests --no-conflicts --no-breaks --no-replaces --no-enhances "$package_name" | grep "^\w" | sort -u)

# Create necessary Packages.gz file
sudo dpkg-scanpackages . | gzip -9c > Packages.gz

# Gzip all of it and ready
tar czvf convoyed.tar.gz .

updated for rhel too:

#!/bin/bash

# Convoy downloads the dependencies for a specified package name for Debian/Ubuntu or RHEL
# Requirements: dpkg-dev for Debian/Ubuntu, yum-utils for RHEL
# Example: ./convoy.sh python3-pip

read -p "Enter the deployment (ubuntu/rhel): " deployment
if [ "$deployment" = "ubuntu" ]; then
  if [ -z "$1" ]; then
    read -p "Enter the package name: " package_name
  else
    package_name="$1"
  fi

  # Get list of dependencies and download
  sudo apt-get download $(apt-cache depends --recurse --no-recommends --no-suggests --no-conflicts --no-breaks --no-replaces --no-enhances "$package_name" | grep "^\w" | sort -u)

  # Create necessary Packages.gz file
  sudo dpkg-scanpackages . | gzip -9c > Packages.gz
else
  if [ -z "$1" ]; then
    read -p "Enter the package name: " package_name
  else
    package_name="$1"
  fi

  # Get list of dependencies and download
  sudo yumdownloader --resolve "$package_name"

  # Create necessary repo file for RHEL
  echo "[local-repo]
name=Local Repository
baseurl=file://<your folder here>/
enabled=1
gpgcheck=0" | sudo tee /etc/yum.repos.d/local-repo.repo >/dev/null
fi

# Gzip all of it and ready
tar czvf convoyed.tar.gz .