There is no "helpful hint" to remember to take engineers if attacking, since the AI may be inconvenient and place field defences either. Neither is there one to remember to buy flak, just in case the enemy is unsporting and buys air.
The River Crossing assault message is given to you up-front, plus it's available on the "Mission" key on the purchase screen as a reminder, and if you actually look at the game map with the "View Map" key - which is just above the mission key on the purchase screen, then you
should notice the great big blue thing smack in the middle of the map?. (I cannot think of any reason to
not examine the game map prior to purchase, and simply buy blind!
)
Andy