1. Legally, the LEO can lie to you without any form of repercussions affecting him. YOU cannot lie to a LEO because if you are caught lying, there are legal repercussions for you.
2, Any lawyer worthy of the title will tell you that you should NEVER consent to a search of your vehicle. If the LEO has probable cause he can search anyway. If he does not have probable cause, you have just set yourself up for a search that the LEO would not normally be able to do.
3. Be civil, but know that the LEO is NOT your friend, your pal, or your buddy. You were stopped for an infraction of the law and possibly an investigation into whether you are involved in something more nefarious, based upon you and your vehicle fitting a certain profile.
4. The courts have ruled that carrying large sums of cash is indicative of drug activity, and the police can and have seized traveler's cash under suspicion of it being the ill gotten gains of drug activity. Then it is up to you to prove otherwise. There is no innocent until proven guilty.
Therefore, I NEvER allow my vehicle to be searched when an officer requests it incident to a traffic stop. If there is probable cause, he will search without having to ask. If he wants to go fishing, make him get a license, in other words, a warrant from a judge.
You have certain rights in this country, and if you do not exercise those rights, they're as good as gone.